Replace String() calls with .toString()/.toLocaleString() per ast-grep rule

- Add formatError() helper in CLI to safely handle unknown error types
- Add uniqueTestId() helper for generating unique test identifiers
- Replace String(id) with id.toString() for database ID conversions
- Replace String(n) with n.toLocaleString() for user-facing number formatting
- Fix TypeScript errors in test files (undefined checks, unused variables)
- Update lint commands to include ast-grep scanning

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api-server/src/index.ts

@@ -45,7 +45,7 @@ Bun.serve({
     if (url.pathname.startsWith("/api/v1/rpc")) {
       // Build context for the request
       const origin =
-        request.headers.get("origin") ?? `http://localhost:${String(port)}`;
+        request.headers.get("origin") ?? `http://localhost:${port.toString()}`;
 
       // Create response headers for setting cookies
       const resHeaders = new Headers();