PR 4b: Apply CA1822 static method modifiers + Gitea Actions secrets guidance

Completed DEBT-001 paydown (1pt) by making three pure-function methods static:
- ScheduleOccurrencePlanner.GetNextDueAt (no instance state accessed)
- PromotionGateEvaluator.Evaluate (evidence gate only, no mutations)
- EvaluationWindowPlanner.Plan (deterministic date calculation)

Changes:
- Added `static` modifier to three domain methods
- Updated call sites: ModelOperationsDispatcherJob, tests
- Removed unnecessary DI registrations (ModelOperationsModule)
- Eliminated instance creation overhead in tests

Test Results: 40/40 PASS (17 ModelOps + 18 SignalEngine + 5 Architecture)

Documentation:
- Updated TECH_DEBT_REGISTER.md: DEBT-001 Completed (PR 4b)
- Added Gitea Actions Secrets section to CLAUDE.md documenting:
  - KRX_API_KEY, OPENDART_API_KEY, KIS_API_KEY storage location
  - CI/CD usage pattern
  - Local dev guidance

Per AGENTS.md v16.0: Code changes are performance improvements, not suppressions.
Quarterly paydown: +1pt (target 4pts for 20% Q3 2026)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Modules.ModelOperations/Scheduling/ModelOperationsDispatcherJob.cs

@@ -12,7 +12,6 @@ public sealed class ModelOperationsDispatcherJob(
     IModelScheduleRepository schedules,
     IBackgroundJobClient jobs,
     IClock clock,
-    ScheduleOccurrencePlanner occurrencePlanner,
     ILogger<ModelOperationsDispatcherJob> logger)
 {
     private static readonly Action<ILogger, string, string, Exception?> LogDispatchFailed =
@@ -42,7 +41,7 @@ public sealed class ModelOperationsDispatcherJob(
                     item.IdempotencyKey));
                 var backgroundJobId = jobs.Create(job, new EnqueuedState(item.Queue));
 
-                var nextDueAt = occurrencePlanner.GetNextDueAt(item.ScheduledFor, item.Cadence, item.CatchUpPolicy, item.MaxCatchUp, now);
+                var nextDueAt = ScheduleOccurrencePlanner.GetNextDueAt(item.ScheduledFor, item.Cadence, item.CatchUpPolicy, item.MaxCatchUp, now);
                 await schedules.MarkDispatchedAsync(
                     item.ScheduleId,
                     leaseOwner,