feat: migrate to Cloudflare Workers with icon and version upload

Replace Express/SQLite and web/ with frontend/, worker/, and wrangler deploy. Add optional app icon upload, date-based app_version, and build-app workflow input.

Co-authored-by: Cursor <cursoragent@cursor.com>

worker/tsconfig.json

@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "lib": ["ES2022"],
+    "types": ["@cloudflare/workers-types"],
+    "strict": true,
+    "skipLibCheck": true,
+    "noEmit": true,
+    "isolatedModules": true
+  },
+  "include": ["src/**/*.ts"]
+}