feat: expose internal contexts and composer components in the public API (#3242)

## Summary

Several components, hooks, and contexts are used internally and
referenced by the docs, but were never re-exported from the package
barrels — so consumers can't import them. This wires them into the
public API. Purely additive barrel re-exports; no behavior change.

## Newly exported

**`src/context/index.ts`**
- `VirtualizedMessageListContext`,
`VirtualizedMessageListContextProvider`,
`useVirtualizedMessageListContext`, `VirtualizedMessageListContextValue`

**`src/components/index.ts`**
- `SummarizedMessagePreview`, `useLatestMessagePreview` (+ its
`ChannelPreviewMessageType`, `ChannelPreviewDeliveryStatus`,
`LatestMessagePreviewData`, `UseLatestMessagePreviewParams` types)

**`src/components/MessageComposer/index.ts`**
- `VoiceRecordingPreviewSlot` (component; only its Props type was
exported before)
- `MessageComposerActions` and `AdditionalMessageComposerActions`

## Why

A docs audit of the v14 React SDK found multiple cookbook/reference
pages instructing readers to import these symbols from
`stream-chat-react`, which fails at runtime because the barrels don't
re-export them. Rather than route the docs around them, expose the
symbols (the docs update is in GetStream/docs-content#1431).

## Notes
- No collisions: none of the newly-exported names are exported
elsewhere.
- `AdditionalMessageComposerActions` and the four
`useLatestMessagePreview` types ride along via `export *` — intentional;
flag if you'd prefer narrower named exports.
- Not exposed (left internal, unchanged): `EditedMessagePreview`,
`SendToChannelCheckbox`, `restorePreEditSnapshot`.

## Checks
- `yarn types` ✅
- `yarn eslint` (changed files) ✅
- Barrel-only change; no tests added. Happy to add export-surface tests
if desired.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **New Features**
  * Added support for voice recording previews in the message composer.
  * Exposed additional message composer actions.
  * Added summarized message preview functionality.
  * Added access to virtualized message list context functionality.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: oliverlaz

src/components/MessageComposer/index.ts

@@ -1,5 +1,8 @@
 export * from './AttachmentSelector';
-export { AttachmentPreviewList } from './AttachmentPreviewList';
+export {
+  AttachmentPreviewList,
+  VoiceRecordingPreviewSlot,
+} from './AttachmentPreviewList';
 export type {
   AttachmentPreviewListProps,
   FileAttachmentPreviewProps,
@@ -16,6 +19,7 @@ export * from './hooks';
 export * from './icons';
 export * from './LinkPreviewList';
 export * from './MessageComposer';
+export * from './MessageComposerActions';
 export * from './MessageComposerUI';
 export * from './QuotedMessagePreview';
 export * from './SendButton';

src/components/index.ts

@@ -38,6 +38,7 @@ export * from './Notifications';
 export * from './Poll';
 export * from './Reactions';
 export * from './SafeAnchor';
+export * from './SummarizedMessagePreview';
 export * from './TextareaComposer';
 export * from './Thread';
 export * from './Threads';

src/context/index.ts

@@ -14,4 +14,5 @@ export * from './ModalContext';
 export * from './PollContext';
 export * from './TranslationContext';
 export * from './TypingContext';
+export * from './VirtualizedMessageListContext';
 export * from './WithComponents';