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>

frontend/tsconfig.json

@@ -0,0 +1,4 @@
+{
+  "files": [],
+  "references": [{ "path": "./tsconfig.app.json" }, { "path": "./tsconfig.node.json" }]
+}