Allow bulk update of movies, music and games

[mforce]

Problem

Right now every field change requires editing items one at a time through the detail view. This is fine for occasional tweaks but becomes tedious for common batch operations like:

• Setting tags on a group of items (e.g. tagging everything acquired in 2025)
• Updating status (e.g. marking 20 movies as "Watched")
• Setting personal rating on recently watched items
• Updating condition, acquisition source, or other shared metadata

Proposed solution

Add a bulk update flow to the collection list pages (Movies, Music, Games):

1. Item selection

• Add a checkbox to each card/row in CollectionList (hidden by default, toggled via a "Select" mode button in the toolbar)
• Support "Select all visible" toggle in the toolbar
• Show selection count in toolbar (e.g. "12 selected")

2. Bulk action bar

• When items are selected, show a floating or inline action bar with:
  • Bulk update… → opens a modal/drawer with fields to update
  • Delete → confirm & delete selected (reuses existing DELETE /api/:type/:id in a batch)

3. Bulk update modal

• Show only the common fields shared across all three types (from CollectionItemBase):
  • Tags (add/remove)
  • Status
  • Personal rating
  • Condition
  • Notes (append mode)
• Plus type-specific fields where it makes sense:
  • Movies: WatchStatus, formats
  • Games: PlayStatus
• Each field shows current value distribution for selected items (e.g. "Status: 8 Owned, 4 Want") to make it clear what is being changed

4. Backend API

New endpoint on each resource group:

PATCH /api/movies/bulk
PATCH /api/music/bulk
PATCH /api/games/bulk

Payload:

{
  "ids": [1, 5, 12, 47],
  "updates": {
    "status": "watched",
    "tags": { "add": ["favorites"], "remove": ["backlog"] },
    "personalRating": 8
  }
}

• Only non-null fields in updates are applied (partial update semantics)
• All items must belong to the current user (OwnerId filter)
• Return count of updated items + any errors per ID (e.g. if an ID was already deleted)

5. Frontend hooks

• New TanStack Query mutation useBulkUpdate(type) in api/
• Selection state managed locally in CollectionList (no URL state needed for MVP)
• Invalidate [type] query key on success to refresh the list

Out of scope (follow-ups)

• Bulk import via CSV (separate issue)
• Bulk cover image updates
• Undo/redo for bulk operations

Verification

• dotnet build clean, npm run build clean
• Select 5+ movies, bulk-update status and tags → confirm DB reflects changes
• Try bulk-updating items owned by another user → rejected (multi-user, Phase 4)
• Try bulk-updating with empty ID list → 400 Bad Request