feat(scheduler-dispatch-commit): add dispatch-fail retry counter to job_t (task 1.3)

Add uint32_t dispatch_fail_count to the job_t wrapper struct (xce/types.h,
alongside submit_lsn, same in-memory-only/reset-on-failover precedent),
per Requirement 4.3. Data model only -- xce_job_t (wire type) untouched,
job.c untouched; increment/reset wiring and the bounded-retry threshold
check are tasks 3.1/3.3.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.kiro/specs/scheduler-dispatch-commit/tasks.md

@@ -15,7 +15,7 @@
   - _Requirements: 2.4_
   - _Boundary: WAL Dispatch Fact_
 
-- [ ] 1.3 (P) Track how many consecutive times a job's dispatch has failed for a retryable reason
+- [x] 1.3 (P) Track how many consecutive times a job's dispatch has failed for a retryable reason
   - Add an in-memory counter on the controller's job record that increments on each retryable dispatch failure and resets to zero on a successful dispatch
   - This counter does not need to survive a controller failover — resetting to zero after a failover is an acceptable, safe degradation
   - Observable completion: the counter can be incremented, read, and reset independently of any actual dispatch attempt