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>

CLAUDE.md

@@ -452,7 +452,30 @@ Before writing code, verify:
 - **Non-value-loss sell:** Requires ReentryWatch, new CycleId/Lot, step intervals, expiry, dedup.
 - **Activation gating:** Requires ModelCard, OOS/PBO/DSR evidence, maker-checker approval, effective_at, rollback justification.
 
-## Gitea API Automation (Optional but Recommended)
+## Gitea API Automation & Actions Secrets
+
+### Gitea Actions Secrets
+
+**External API keys are stored in Gitea Actions Secrets (not in .env or code).**
+
+**Location:** `https://gitea.taxbaik.com/kjh2064/KArtSell.Aegis/settings/actions/secrets`
+
+**Available secrets:**
+- `KRX_API_KEY` — Korea Exchange data feed (market calendar, trading sessions)
+- `OPENDART_API_KEY` — OpenDart financial disclosure API
+- `KIS_API_KEY` — Korea Investment & Securities trading API
+
+**Usage in CI/CD (`.gitea/workflows/*.yml`):**
+```yaml
+env:
+  KRX_API_KEY: ${{ secrets.KRX_API_KEY }}
+  OPENDART_API_KEY: ${{ secrets.OPENDART_API_KEY }}
+  KIS_API_KEY: ${{ secrets.KIS_API_KEY }}
+```
+
+**For local development:** Ask team lead for local sandbox keys or use mock fixtures in tests.
+
+### Gitea API Automation (Optional but Recommended)
 
 ### Environment Setup