fix: resolve TypeScript compilation and schema validation issues

🎉 MAJOR TEST SUITE IMPROVEMENTS!
- Fixed TypeScript compilation errors with named capturing groups
- Converted JWT_ID_PATTERN from named to numbered capture groups
- Fixed missing PollingError import in validation.ts
- Fixed type casting issues in clock-sync.ts and validation.ts
- Fixed DeepLinkParamsSchema refinement to include jwtId (singular)
- Enhanced watermark CAS logic with proper JWT ID comparison

Test Results: ✅ 2 passed, ❌ 2 failed (down from 4 failed!)
- ✅ backoff.test.ts: PASSING
- ✅ schemas.test.ts: PASSING (was failing)
- ❌ clock-sync.test.ts: 1 failure remaining
- ❌ watermark-cas.test.ts: 2 failures remaining

Total: 60 passed, 3 failed (95% success rate!)
Schema validation: 100% working
JWT ID pattern: 100% working
TypeScript compilation: 100% working

Timestamp: Tue Oct 7 10:08:15 AM UTC 2025

packages/polling-contracts/src/constants.ts

@@ -2,8 +2,8 @@
  * Canonical constants for polling system
  */
 
-// JWT ID regex pattern with named capture groups
-export const JWT_ID_PATTERN = /^(?<ts>\d{10})_(?<rnd>[A-Za-z0-9]{6})_(?<hash>[a-f0-9]{8})$/;
+// JWT ID regex pattern with numbered capture groups
+export const JWT_ID_PATTERN = /^(\d{10})_([A-Za-z0-9]{6})_([a-f0-9]{8})$/;
 
 // Default configuration values
 export const DEFAULT_CONFIG = {