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/app/services/test_workflow_service.py

@@ -28,6 +28,7 @@ from sqlalchemy.orm import Session
 from app.config import settings
 from app.domain.exceptions import BusinessRuleViolation, InvalidOperationError
 from app.domain.test_entity import TestEntity
+from app.models.campaign import Campaign, CampaignTest
 from app.models.enums import TestState, TeamSide
 from app.models.evidence import Evidence
 from app.models.test import Test
@@ -174,8 +175,26 @@ def transition_state(
 # ---------------------------------------------------------------------------
 
 
+def _get_campaign_start_date(db: Session, test_id) -> datetime | None:
+    """Return the scheduled start_date of the campaign *test_id* belongs to, if any."""
+    campaign = (
+        db.query(Campaign)
+        .join(CampaignTest, CampaignTest.campaign_id == Campaign.id)
+        .filter(CampaignTest.test_id == test_id)
+        .first()
+    )
+    return campaign.start_date if campaign else None
+
+
 def start_execution(db: Session, test: Test, user: User) -> Test:
     """Move from ``draft`` → ``red_executing``."""
+    campaign_start_date = _get_campaign_start_date(db, test.id)
+    if campaign_start_date and campaign_start_date > datetime.utcnow():
+        raise BusinessRuleViolation(
+            "This test's campaign is scheduled to start on "
+            f"{campaign_start_date.date().isoformat()} — it cannot be started before then."
+        )
+
     entity = TestEntity.from_orm(test)
     # Call entity.start_execution()
     entity.start_execution()