feat: bearer auth, auto-sync events, test seed

- Add bearer plugin to BetterAuth for mobile auth
- Auto-sync birthday/anniversary events on client create/update
- Add /api/events/sync-all endpoint for bulk sync
- Add test user seed (test@test.com / test)
- Expose set-auth-token header in CORS

src/lib/auth.ts

@@ -1,4 +1,5 @@
 import { betterAuth } from 'better-auth';
+import { bearer } from 'better-auth/plugins';
 import { drizzleAdapter } from 'better-auth/adapters/drizzle';
 import { db } from '../db';
 import * as schema from '../db/schema';
@@ -13,6 +14,9 @@ export const auth = betterAuth({
       verification: schema.verifications,
     },
   }),
+  plugins: [
+    bearer(), // Enable bearer token auth for mobile apps
+  ],
   emailAndPassword: {
     enabled: true,
     requireEmailVerification: false, // Enable later for production