feat(web): add duplicate playlist flow under the New nav button (#14319)

## Summary

Adds a **Duplicate Playlist** secondary action to the sidebar's `+`
(New) popup menu. Users paste any public Audius playlist URL, see a
preview of the source (title, description, cover art), and toggle
per-field switches to choose what to customize in the copy. The
duplicated playlist is created as private by default.

Stacks on top of #14318 (Create Playlist modal) — review/merge that
first.

**Scope:**
- Metadata-only duplication for v1: title, description, artwork. Tracks
are **not** copied in this PR — a follow-up will support full duplicate
including track contents. The modal surfaces this with a helper line so
users know to add tracks themselves.
- When the user keeps the source artwork, we pass the source's
`cover_art_sizes` CID through to the existing `createPlaylist` saga so
it reuses the cover instead of treating it as a new upload. No content
node re-upload required.

## Implementation
- New `DuplicatePlaylistModal` Redux modal slice (via existing
`createModal` helper) registered in modals types/reducers/parent state.
- New `DuplicatePlaylistModal` component using Harmony `Modal` +
`TextInput` + `Switch` + `TextArea` + `Artwork` + the existing
`UploadArtwork`.
- URL paste resolves through `getPathFromPlaylistUrl` →
`useCollectionByPermalink` to load the source collection.
- Wires "Duplicate Playlist" into `CreatePlaylistLibraryItemButton`
between Create Playlist and Create Folder.

## Test plan

- [ ] Sign in to the web app
- [ ] Left nav → `+` → **Duplicate Playlist**
- [ ] Paste a malformed URL → see inline "Enter a valid Audius playlist
URL"
- [ ] Paste a valid Audius playlist URL → preview card appears with the
source title, description, and artwork
- [ ] Submit with all three switches off → new playlist created with
`<Source Title> (Copy)`, the source description, and the source cover
art reused (no re-upload)
- [ ] Toggle "Customize title" → enter a custom name → that name wins
- [ ] Toggle "Customize description" → enter a custom description → that
description wins
- [ ] Toggle "Customize artwork" → upload a new image → custom image
wins
- [ ] Resulting playlist is private (Hidden) and the user is routed to
its edit page
- [ ] The "tracks not copied" note is visible in the modal

## Follow-ups
- Copy tracks from source to the duplicated playlist (probably via a new
`duplicatePlaylist` action + saga that chains `createPlaylist` then
`addTrackToPlaylist` per track).
- Paste-tracks-by-URL on the edit page (separate PR), which pairs
naturally with this once track copy lands.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: dylanjeffers

packages/common/src/store/ui/modals/duplicate-playlist-modal/index.ts

@@ -0,0 +1,20 @@
+import { createModal } from '../createModal'
+
+export type DuplicatePlaylistModalState = {
+  isAlbum?: boolean
+}
+
+const duplicatePlaylistModal = createModal<DuplicatePlaylistModalState>({
+  reducerPath: 'DuplicatePlaylistModal',
+  initialState: {
+    isOpen: false,
+    isAlbum: false
+  },
+  sliceSelector: (state) => state.ui.modals
+})
+
+export const {
+  hook: useDuplicatePlaylistModal,
+  reducer: duplicatePlaylistModalReducer,
+  actions: duplicatePlaylistModalActions
+} = duplicatePlaylistModal

packages/common/src/store/ui/modals/index.ts

@@ -42,3 +42,4 @@ export * from './send-tokens-modal'
 export * from './coin-success-modal'
 export * from './fan-club-details-modal'
 export * from './create-playlist-modal'
+export * from './duplicate-playlist-modal'

packages/common/src/store/ui/modals/parentSlice.ts

@@ -85,7 +85,8 @@ export const initialState: BasicModalsState = {
   FanClubDetailsModal: { isOpen: false },
   VerificationSuccess: { isOpen: false },
   VerificationError: { isOpen: false },
-  CreatePlaylistModal: { isOpen: false }
+  CreatePlaylistModal: { isOpen: false },
+  DuplicatePlaylistModal: { isOpen: false }
 }
 
 const slice = createSlice({

packages/common/src/store/ui/modals/reducers.ts

@@ -15,6 +15,7 @@ import { createChatModalReducer } from './create-chat-modal'
 import { createPlaylistModalReducer } from './create-playlist-modal'
 import { deleteTrackConfirmationModalReducer } from './delete-track-confirmation-modal'
 import { downloadTrackArchiveModalReducer } from './download-track-archive-modal'
+import { duplicatePlaylistModalReducer } from './duplicate-playlist-modal'
 import { earlyReleaseConfirmationModalReducer } from './early-release-confirmation-modal'
 import { editAccessConfirmationModalReducer } from './edit-access-confirmation-modal'
 import { externalWalletSignUpModalReducer } from './external-wallet-sign-up-modal'
@@ -94,7 +95,8 @@ const combinedReducers = combineReducers({
   SendTokensModal: sendTokensModalReducer,
   CoinSuccessModal: coinSuccessModalReducer,
   FanClubDetailsModal: fanClubDetailsModalReducer,
-  CreatePlaylistModal: createPlaylistModalReducer
+  CreatePlaylistModal: createPlaylistModalReducer,
+  DuplicatePlaylistModal: duplicatePlaylistModalReducer
 })
 
 /**

packages/common/src/store/ui/modals/types.ts

@@ -121,6 +121,7 @@ export type Modals =
   | 'VerificationSuccess'
   | 'VerificationError'
   | 'CreatePlaylistModal'
+  | 'DuplicatePlaylistModal'
 
 export type BasicModalsState = {
   [modal in Modals]: BaseModalState