fix: Resolve all TypeScript build errors — path aliases + unused params

Adds baseUrl and @/* path mapping to tsconfig.app.json so vue-tsc can
resolve @/types, @/stores, and @/composables. Prefixes unused stub
parameters with _ to satisfy noUnusedParameters. Full build now passes.

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

frontend/tsconfig.app.json

@@ -3,6 +3,10 @@
   "compilerOptions": {
     "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
     "types": ["vite/client"],
+    "baseUrl": ".",
+    "paths": {
+      "@/*": ["./src/*"]
+    },
 
     /* Linting */
     "strict": true,