feat: add project files REST endpoints with auth and audit logging

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/types/index.ts

@@ -126,4 +126,5 @@ export type EntityType =
   | 'vehicle'
   | 'bank_account'
   | 'company_settings'
-  | 'leave_balance';
+  | 'leave_balance'
+  | 'project_file';