Phase 9: homebrew content + packs

- Homebrew entity (monster/spell/item/feat/condition) — Dexie v6, repo, hook,
  cascade-deleted with campaign
- Homebrew editor page: per-kind fields + description, create/edit/delete
- Compendium merges campaign homebrew of the matching kind (HB badge, generic
  HomebrewDetail) with the same cross-links (add monster->combat, spell/item->character)
- Content packs: export/import homebrew as JSON (validated, ids reassigned)
- System extensibility documented via the existing RulesSystem registry seam
- Fix: card editors (homebrew/npc/quest/note) debounce-save the FULL snapshot, not
  partial patches — editing two fields fast no longer drops an edit

New homebrew e2e + cascade test coverage.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/features/world/DashboardPage.tsx

@@ -21,6 +21,7 @@ const LINKS = [
   { to: '/maps', label: 'Maps', icon: '🗺️' },
   { to: '/calendar', label: 'Calendar', icon: '📅' },
   { to: '/compendium', label: 'Compendium', icon: '📚' },
+  { to: '/homebrew', label: 'Homebrew', icon: '🛠️' },
   { to: '/dice', label: 'Dice', icon: '🎲' },
   { to: '/play', label: 'Player View', icon: '📺' },
 ] as const;