feat(run-store): implement reschedule, debounce, metadata, idempotency-clear, and array-append methods

Replaces the seven throwing stubs in PostgresRunStore with verbatim-relocated
Prisma statements sourced from delayedRunSystem, debounceSystem, updateMetadata,
idempotencyKeys, resetIdempotencyKey, batchTriggerV3, and the realtime-stream
route handlers.

- rescheduleRun: writes delayUntil always; queueTimestamp when provided; nested
  DELAYED executionSnapshot when snapshot arg provided
- enqueueDelayedRun: sets status PENDING + queuedAt
- rewriteDebouncedRun: pass-through update with associatedWaitpoint include
- updateMetadata: optimistic-lock path (updateMany with version predicate) or
  direct path (update without predicate); both return { count }
- clearIdempotencyKey: three discriminated-union branches — byId clears both
  columns, byPredicate clears both, byFriendlyIds clears only idempotencyKey
- pushTags: push-append to runTags array; returns { updatedAt }
- pushRealtimeStream: push-append to realtimeStreams array; returns void

Author: d-cs