fix(mobile): guard comment components against undefined track from lineup cache

[dylanjeffers]

What

Hardens the comment-drawer components against an undefined track when the drawer is opened from a lineup/feed track tile (where the track is hydrated from the partial lineup cache, not the full track-screen fetch).

• CommentBlock: bail with if (!track) return null before CommentBlockInternal dereferences track.track_id / track.pinned_comment_id / track.duration.
• CommentOverflowMenu: optional-chain the context track accesses (track?.pinned_comment_id, track?.permalink).

Why

The comment section context types track as always-present (track: Track) and the provider returns null until the track loads — so under normal flow these are safe. This is belt-and-suspenders hardening for the tile-open path, the same family as the already-merged crash fixes:

• fix(mobile): prevent crash when posting a comment #14490 — CommentThread.rootComment.id
• fix(mobile): prevent comment drawer crash on open from unguarded track access #14492 — ComposerInput.partialTrack.access?.stream

Note on the live RC crash

While investigating I found the current release-candidate branches (release-client-v*, up to v1.5.164) do not contain #14490 or #14492 — both merged to main on Jun 16–17. If testers are still crashing on the comment button, the most likely cause is that the RC build predates those fixes, independent of this PR. Worth confirming the RC's build commit / CodePush channel.

Test plan

• npx tsc --noEmit (packages/mobile) — clean
• npx eslint on both files — clean

🤖 Generated with Claude Code

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[dylanjeffers]

Closing as redundant — CommentSectionProvider already returns null when track is undefined (commentsContext.tsx:230), so CommentBlock and CommentOverflowMenu as provider children can never see an undefined track. The underlying blank-drawer root cause was fixed in #14494, which gates the drawer itself on the loaded track. This PR's guards would be dead code.