feat(engagement): video dislike + creator heart + creator pin

Three features that depend on the two additive migrations shipped in
the same commit (safe defaults, cascading foreign keys, no data loss
possible).

## Dislike button
- New video_dislikes table (migration 2026_10_21_000001) with the same
  shape as video_likes.
- Video model: dislikes() relation + isDislikedBy() / getDislikeCount
  Attribute() helpers mirroring the like pair.
- UserController@toggleDislike: endpoint behind POST
  /videos/{video}/toggle-dislike. Mutually exclusive with like — the
  toggle*Like / toggle*Dislike controllers detach the opposite state
  so a user is in exactly one of {liked, disliked, neither}. YouTube
  parity.
- video-actions component: a second thumbs-down button next to the
  existing like. Both reconcile in parallel on either response so the
  UI pair always reflects the authoritative server state.

## Creator heart + pin
- comments table gains hearted + pinned boolean columns (migration
  2026_10_21_000002, both default false, pinned is indexed).
- CommentController@heart + @pin: 403 for anyone but the video owner;
  pin() also rejects nested replies (422) and auto-unpins the
  previously-pinned top-level comment so the "at most one pinned"
  invariant is enforced at the DB level.
- Comment component:
    - Pinned comments render ahead of everything else; reorder()
      clears the comments() relation's default ->latest() so pinned
      DESC becomes the PRIMARY sort instead of a tiebreaker.
    - Creator sees heart + pin toggle buttons in the action bar.
    - Hearted comments carry a small red heart badge in the meta row.
    - Pinned comments carry a "Pinned by {creator}" header and a
      red left accent so they're visually distinct from the stream.

## Tests (9 new, 63 total)
- Dislike toggle adds/removes the row.
- Disliking clears an existing like and vice versa.
- Owner can heart; non-owner gets 403.
- Only one comment pinned at a time; replies can't be pinned (422);
  non-owner gets 403.
- Pinned comments render before newer unpinned ones.

## Deploy note
Running the migrations against the live DB needs:
    php artisan migrate

The two migration files are additive and reversible via `migrate:rollback`.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

app/Models/Comment.php

@@ -11,6 +11,13 @@ class Comment extends Model
         'user_id',
         'parent_id',
         'body',
+        'hearted',
+        'pinned',
+    ];
+
+    protected $casts = [
+        'hearted' => 'boolean',
+        'pinned'  => 'boolean',
     ];
 
     // Relationships