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>

tests/KArtSell.ModelOperations.UnitTests/EvaluationWindowPlannerTests.cs

@@ -4,8 +4,7 @@ public sealed class EvaluationWindowPlannerTests
 {
     [Fact] public void Uses_trading_sessions_not_calendar_days()
     {
-        var planner = new EvaluationWindowPlanner();
-        var due = planner.Plan("KRX", new DateOnly(2026, 8, 3), new WeekdayCalendar());
+        var due = EvaluationWindowPlanner.Plan("KRX", new DateOnly(2026, 8, 3), new WeekdayCalendar());
         Assert.Equal(new[] { 1, 5, 20, 63, 126, 252 }, due.Select(x => x.WindowTradingDays));
         Assert.All(due, x => Assert.DoesNotContain(x.DueSession.DayOfWeek, new[] { DayOfWeek.Saturday, DayOfWeek.Sunday }));
     }