feat(backend): enforce campaign scheduling, add reviewer queue filter, tactic order, duplicate-test counts

- start_execution now blocks a test from starting before its campaign's
  start_date, closing a gap where the field was persisted but never
  enforced
- GET /tests gains a reviewer_id "my reviews" filter for the red_review/
  blue_review lead-gate stage, distinct from pending_validation_side
  (which only ever covered the later in_review stage and ignored
  assignment entirely)
- get_coverage_by_tactic now returns all 14 MITRE tactics in canonical
  kill-chain order instead of an alphabetical, partial list — the
  regular Dashboard and Executive Dashboard both consume this endpoint
  and previously disagreed on order/completeness
- test-template listing now includes existing_test_count per technique
  so the catalog can warn before creating a likely-duplicate test

backend/tests/test_t106_workflow_service.py

@@ -60,7 +60,11 @@ def _make_user(role: str = "red_tech") -> MagicMock:
 
 
 def _make_db() -> MagicMock:
-    return MagicMock()
+    db = MagicMock()
+    # start_execution's campaign-schedule lookup (.query(Campaign).join(...).filter(...).first())
+    # defaults to "no campaign found" so unrelated tests aren't gated by a MagicMock date.
+    db.query.return_value.join.return_value.filter.return_value.first.return_value = None
+    return db
 
 
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