feat(composer): edit shared posts and share-to-squad in the new composer - #6422

Editing a shared link still opened the old /posts/[id]/edit page: the
menu only routed freeform and welcome posts to SmartComposerModal, and
the modal forced kind to 'text' whenever editPost was set, so it could
not represent a share at all.

- Derive the kind from editPost.type, prefill the commentary the way the
  old page did (a share with no commentary carries the shared post's own
  title, which is not the author's text), and seed the preview from the
  post rather than refetching it
- Lock the URL while editing: only the commentary is editable, matching
  what the API accepts
- Add the missing edit branch to submitLink, including the moderation
  path, which completes without a toast of its own
- Route share posts to the modal; moderation items keep the page, which
  edits a pending submission the composer cannot represent
- Delete CreateLiveRoomForm and CreatePoll, referenced by nothing

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Squad share triggers (ShareBar, DiscussionShareRow, Share modal) now open
SmartComposerModal seeded with the post as the link preview and the squad
preselected, replacing CreateSharedPostModal. The composer's link flow
already covers internal shares (preview.id -> addPostToSquad, moderation,
multi-squad via sharedPostId), so the old modal is deleted along with its
lazy-modal registration. A new onPosted callback carries the ShareToSquad
analytics event that the old modal's onSharedSuccessfully used to fire.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

A composer opened pre-filled (share-to-squad, ?share= deep links) counted
its own seed as unsaved changes, so closing it untouched asked to discard
a draft the user never wrote.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Comments explaining what the code already says, narrating fixed bugs, or
restating test names are removed; the ones that survive state constraints
the code cannot show (platform quirks, cross-file contracts, do-not-readd
traps).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

- share-edit save now shows its in-flight state (isUpdatePostLoading joins
  isPosting)
- the mobile composer drawer portals to the root, so opening it from the
  Share modal's drawer no longer traps it in a transformed ancestor
- editing always targets the post's own source instead of falling back to
  the personal audience when the squad is no longer postable
- a moderated share edit is no longer logged as a post creation
- the share-edit dirty check trims like the seed comparison does
- a locked link with no surviving shared post renders no empty preview card
- CommentMarkdownInput skips the visualViewport subscription when it fills
  its container (the value was discarded)
- the locked-link no-refetch spec now actually exercises the guard

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Live verification found two defects: a freeform post with no body (title +
cover) could never save a title edit because submit demanded a body, and
the desktop 'Add a comment' composer opened unfocused — the by-id focus
helper races the lazy chunk and TipTap's async editor, so the composer now
owns its focus through the queued autofocus path.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

…t-post-new-composer

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

…2e164b' into claude/edit-post-new-composer

…2e164b' into claude/edit-post-new-composer

…t-post-new-composer

The submit helpers now take the narrowed Squad instead of casting
primary ten times, the createMulti payloads drop their as-unknown
casts (they already match CreatePostInMultipleSourcesArgs), and the
defaultWriteTab key lookup uses a type guard instead of a double cast.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>