Apply Design A: dark theme, type badges, code cleanup

Visual:
- Dark theme throughout (#111 bg, #1c1c1c panels, #2a2a2a borders)
- Type badges with color: Monster=orange, Spell=green, Trap=purple
- Owned count shown as ×3 (highlighted) or — (dimmed)
- Printing column headers in CardRow
- Card detail panel: type badge, attribute, race, level stars

Cleanup:
- Replace index.css (was Vite boilerplate) with dark base + shared CSS classes
  (.card-row-header:hover, .filter-chip, .icon-btn, modal styles)
- Clear App.css (Vite boilerplate, unused)
- Remove Footer.css (modal styles consolidated into index.css)
- Extract useDebounce to src/hooks/useDebounce.js
- Remove react-window (installed but never used)
- App.jsx: remove unnecessary wrapper div
- gitignore: add mockups/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -12,8 +12,7 @@
   "dependencies": {
     "react": "^19.2.4",
     "react-dom": "^19.2.4",
-    "react-virtuoso": "^4.18.3",
-    "react-window": "^2.2.7"
+    "react-virtuoso": "^4.18.3"
   },
   "devDependencies": {
     "@eslint/js": "^9.39.4",