docs(ui)!: correct migration docs; remove dead MessageDetails (#2680)

* update migration docs with latest changes

* Add migration doc for sort option

* docs: correct migration docs against verified source

Apply ~70+ corrections across all 16 redesign migration docs and
v10-migration.md based on a source-by-source verification pass. Fixes
non-existent symbols, wrong constructor params, wrong typedef
signatures, and stale class names that would prevent migration code
examples from compiling. Adds the missing ClientState collection
immutability breaking-change section (introduced in 2501f53).

Also cleans up five stale dartdoc references in source that seeded
some of the wrong names in the docs (StreamMessagePlacement →
StreamMessageLayout, UrlAttachmentBuilder → LinkPreviewAttachmentBuilder,
StreamChat(config:) → streamChatConfigData:, etc.).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* refactor(ui)!: remove unused MessageDetails class

The MessageDetails class was only used by itself — no live consumers in
packages/ or sample_app. The new messageBuilder signature stopped passing
it as an argument, leaving the class as dead public surface area. Delete
the file and its export; update CHANGELOG and the migration doc that
previously said "no longer passed to builders" to reflect the actual
removal.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* feat(ui): re-export StreamAvatarTheme/Data from stream_core_flutter

The two avatar theme types live in stream_core_flutter, but consumers
who only depended on stream_chat_flutter had to add a second import to
theme avatars globally. Add them to the show allowlist so existing
StreamAvatarThemeData imports keep working, drop the now-redundant
stream_core_flutter import from stream_media_gallery_item.dart, and
update the migration doc that previously instructed users to import
from stream_core_flutter directly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* chore(ui): inline AttachmentPickerOptionsBuilder typedef, drop empty file

stream_attachment_picker_bottom_sheet.dart only held the
AttachmentPickerOptionsBuilder typedef — the filename implied a sheet
class that no longer exists after pickers became inline. Move the
typedef into stream_attachment_picker.dart (next to the picker widgets
and builder functions that use it) and delete the misleading file.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: add Stream Core / Stream Chat preamble to redesign README

Front-load the two-layer split so future doc passes don't conflate
"moved to stream_core_flutter" with "removed." Includes a small
core-primitive ↔ chat-wrapper table and a "frequently confused names"
list covering the wrong-name patterns that surfaced during the
verification pass (StreamMessagePlacement → StreamMessageLayout,
kStreamHeaderHeight → kStreamToolbarHeight, etc.).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: address CodeRabbit review comments

- attachments_and_polls.md: fix stale #streamattachmentpickeroption
  anchor (→ #attachment-picker) and drop reference to the removed
  showStreamAttachmentPickerModalBottomSheet function.
- v10-migration.md: stable-release boundary was beta.12, not beta.13
  (matches the upgrade matrix at the top of the doc).
- message_actions.md: drop StreamMessageReactionsModal from the
  showStreamDialog Future<T?> "returns" list — the class is deleted.
- message_composer.md: destructure cooldownTimeOut from
  SlowModePlaceholder so translations.slowModeOnLabel(int) gets its
  required argument; matches the source dartdoc example verbatim.

The fourth flagged comment (onDismissTap row in unread_indicator_button.md)
was already removed in the earlier verification pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs(ui): use American spelling "customization" in reaction_picker.md

Line 31 used British "customisation" while the rest of the doc (and the
heading at line 299) uses American "Customization". Match the rest.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fixed last StreamMessagePlacement occurrence

---------

Co-authored-by: Sahil Kumar <xdsahil@gmail.com>
Co-authored-by: Sahil Kumar <sahil@getstream.io>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 3 people

migrations/redesign/README.md

@@ -12,6 +12,29 @@ The redesigned components aim to provide:
 
 Each component migration guide contains specific details about the changes and how to migrate.
 
+## Package Architecture: Stream Core + Stream Chat
+
+The redesigned components are split across two packages:
+
+- **`stream_core_flutter`** — product-agnostic primitives: avatars, badges, buttons, sheets, app bars, message layout, reaction picker, and theming tokens. None of these classes depend on chat-domain models (`Channel`, `Message`, `User`).
+- **`stream_chat_flutter`** — chat-domain wrappers that take chat models and delegate visuals to the primitives.
+
+Most core types are re-exported from `stream_chat_flutter`, so a single `package:stream_chat_flutter/stream_chat_flutter.dart` import is usually enough. When a migration doc says a type "moved to `stream_core_flutter`," it has **not** been removed — it has been re-homed to the primitives layer and (in most cases) re-exported here so existing imports keep working.
+
+### Core primitive ↔ chat wrapper
+
+| Core (in `stream_core_flutter`)                          | Chat wrapper (in `stream_chat_flutter`)                                                     |
+| -------------------------------------------------------- | ------------------------------------------------------------------------------------------- |
+| `StreamAvatar`, `StreamAvatarGroup`, `StreamAvatarStack` | `StreamUserAvatar`, `StreamUserAvatarGroup`, `StreamUserAvatarStack`, `StreamChannelAvatar` |
+| `StreamReactionPicker` (takes `StreamReactionPickerItem`s) | `StreamMessageReactionPicker` (takes `Message`)                                            |
+| `StreamReactions` (takes `ReactionGroup`s)                 | `StreamMessageReactions` (takes `Message`)                                                  |
+
+### Frequently confused names
+
+- `StreamMessageLayout` — **not** `StreamMessagePlacement`.
+- `kStreamToolbarHeight` — **not** `kStreamHeaderHeight`.
+- `StreamAvatarTheme` / `StreamAvatarThemeData` — live in `stream_core_flutter`, re-exported from `stream_chat_flutter`; existing imports continue to work.
+
 ## Theming
 
 The redesigned components use `StreamTheme` for theming. If no `StreamTheme` is provided, a default theme is automatically created based on `Theme.of(context).brightness` (light or dark mode).
@@ -118,23 +141,24 @@ class MyCustomButton extends StatelessWidget {
 
 ## Components
 
-| Component | Migration Guide |
-|-----------|-----------------|
-| Stream Avatar | [stream_avatar.md](stream_avatar.md) |
-| Channel List Item | [channel_list_item.md](channel_list_item.md) |
-| Message Actions | [message_actions.md](message_actions.md) |
-| Reaction Picker / Reactions | [reaction_picker.md](reaction_picker.md) |
-| Image CDN & Thumbnails | [image_cdn.md](image_cdn.md) |
-| Message Widget & Message List | [message_widget.md](message_widget.md) |
-| Message Composer | [message_composer.md](message_composer.md) |
-| Unread Indicator | [unread_indicator.md](unread_indicator.md) |
-| Unread Indicator Button | [unread_indicator_button.md](unread_indicator_button.md) |
-| Reaction List & Detail Sheet | [reaction_list.md](reaction_list.md) |
-| Audio Waveform Theme | [audio_theme.md](audio_theme.md) |
-| Attachments & Polls | [attachments_and_polls.md](attachments_and_polls.md) |
-| Media Viewer (Full-screen Media) | [media_viewer.md](media_viewer.md) |
-| Headers, Icons & Configuration | [headers_and_icons.md](headers_and_icons.md) |
-| Localizations | [localizations.md](localizations.md) |
+| Component                        | Migration Guide                                          |
+| -------------------------------- | -------------------------------------------------------- |
+| Stream Avatar                    | [stream_avatar.md](stream_avatar.md)                     |
+| Channel List Item                | [channel_list_item.md](channel_list_item.md)             |
+| Message Actions                  | [message_actions.md](message_actions.md)                 |
+| Reaction Picker / Reactions      | [reaction_picker.md](reaction_picker.md)                 |
+| Image CDN & Thumbnails           | [image_cdn.md](image_cdn.md)                             |
+| Message Widget                   | [message_widget.md](message_widget.md)                   |
+| Message List                     | [message_list.md](message_list.md)                       |
+| Message Composer                 | [message_composer.md](message_composer.md)               |
+| Unread Indicator                 | [unread_indicator.md](unread_indicator.md)               |
+| Unread Indicator Button          | [unread_indicator_button.md](unread_indicator_button.md) |
+| Reaction List & Detail Sheet     | [reaction_list.md](reaction_list.md)                     |
+| Audio Waveform Theme             | [audio_theme.md](audio_theme.md)                         |
+| Attachments & Polls              | [attachments_and_polls.md](attachments_and_polls.md)     |
+| Media Viewer (Full-screen Media) | [media_viewer.md](media_viewer.md)                       |
+| Headers, Icons & Configuration   | [headers_and_icons.md](headers_and_icons.md)             |
+| Localizations                    | [localizations.md](localizations.md)                     |
 
 ## Need Help?