Add PWA icon generation and Grimoire logo component (#214)

* feat: add Grimoire logo SVG and generate PWA assets

- Add logo.svg with the official Grimoire logo and gradient
- Create GrimoireLogo React component for use in the app
- Add scripts/generate-pwa-icons.mjs to generate all PWA icons from SVG
- Regenerate all favicon and PWA icons from the new logo
- Update mobile welcome screen to show the logo instead of text

* feat: use transparent backgrounds for PWA icons and add theme gradient option

- Update generate-pwa-icons.mjs to output PNGs with transparent backgrounds
- Add gradient prop to GrimoireLogo component ("original" or "theme")
- Theme gradient matches text-grimoire-gradient CSS (yellow -> orange -> purple -> cyan)
- Mobile welcome screen now uses theme gradient to match ASCII art

* feat: use original gradient for mobile welcome logo

---------

Co-authored-by: Claude <noreply@anthropic.com>

package.json

@@ -14,7 +14,8 @@
     "preview": "vite preview",
     "test": "vitest",
     "test:ui": "vitest --ui",
-    "test:run": "vitest run"
+    "test:run": "vitest run",
+    "generate-icons": "node scripts/generate-pwa-icons.mjs"
   },
   "dependencies": {
     "@radix-ui/react-accordion": "^1.2.12",
@@ -112,6 +113,7 @@
     "jsdom": "^27.4.0",
     "postcss": "^8.4.49",
     "prettier": "^3.7.4",
+    "sharp": "^0.34.5",
     "tailwindcss": "^3.4.17",
     "typescript": "~5.6.2",
     "typescript-eslint": "^8.18.2",