feat(polling-contracts): add generic polling interface with TypeScript types and Zod schemas

- Add @timesafari/polling-contracts package with comprehensive type definitions
- Implement GenericPollingRequest, PollingResult, and PollingScheduleConfig interfaces
- Add Zod schemas for StarredProjectsRequest/Response and DeepLinkParams validation
- Include calculateBackoffDelay utility with unified retry policy (exponential, linear, fixed)
- Add OutboxPressureManager for storage pressure controls and back-pressure signals
- Implement TelemetryManager with cardinality budgets and PII redaction
- Add ClockSyncManager for JWT timestamp validation and skew tolerance
- Include comprehensive unit tests with Jest snapshots and race condition testing
- Add JWT_ID_PATTERN regex for canonical JWT ID format validation
- Support idempotency with X-Idempotency-Key enforcement
- Implement watermark CAS (Compare-and-Swap) for race condition prevention

This establishes the foundation for the new generic polling system where host apps
define request/response schemas and the plugin provides robust polling logic.

packages/polling-contracts/src/constants.ts

@@ -0,0 +1,53 @@
+/**
+ * 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})$/;
+
+// Default configuration values
+export const DEFAULT_CONFIG = {
+  // Outbox pressure controls
+  maxUndelivered: 1000,
+  backpressureThreshold: 0.8,
+  maxRetries: 3,
+  cleanupIntervalMs: 3600000, // 1 hour
+  
+  // Backoff policy
+  baseDelayMs: 1000,
+  maxDelayMs: 30000,
+  jitterFactor: 0.25,
+  respectRetryAfter: true,
+  retryAfterMaxMs: 300000, // 5 minutes
+  
+  // Clock sync
+  maxClockSkewSeconds: 30,
+  skewCheckIntervalMs: 300000, // 5 minutes
+  jwtClockSkewTolerance: 30,
+  jwtMaxAge: 3600000, // 1 hour
+  
+  // Telemetry
+  metricsPrefix: 'starred_projects',
+  logLevel: 'INFO'
+} as const;
+
+// Error codes
+export const ERROR_CODES = {
+  INVALID_REQUEST: 'INVALID_REQUEST',
+  VALIDATION_ERROR: 'VALIDATION_ERROR',
+  RATE_LIMIT_EXCEEDED: 'RATE_LIMIT_EXCEEDED',
+  EXECUTION_ERROR: 'EXECUTION_ERROR',
+  CLOCK_SKEW_ERROR: 'CLOCK_SKEW_ERROR',
+  STORAGE_PRESSURE: 'STORAGE_PRESSURE'
+} as const;
+
+// HTTP status codes
+export const HTTP_STATUS = {
+  OK: 200,
+  BAD_REQUEST: 400,
+  UNAUTHORIZED: 401,
+  FORBIDDEN: 403,
+  TOO_MANY_REQUESTS: 429,
+  INTERNAL_SERVER_ERROR: 500,
+  SERVICE_UNAVAILABLE: 503
+} as const;