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_template_service.py

@@ -16,6 +16,8 @@ from app.domain.errors import EntityNotFoundError
 
 # Import TestTemplate from app.models.test_template
 from app.models.test_template import TestTemplate
+from app.models.technique import Technique
+from app.models.test import Test
 
 # Import escape_like from app.utils
 from app.utils import escape_like
@@ -91,6 +93,21 @@ def list_templates(
         # Chain .all() call
         .all()
     )
+
+    # Attach existing_test_count per template — lets the catalog warn before
+    # creating a likely-duplicate test for a technique that already has one.
+    if templates:
+        mitre_ids = {t.mitre_technique_id for t in templates}
+        counts = dict(
+            db.query(Technique.mitre_id, func.count(Test.id))
+            .join(Test, Test.technique_id == Technique.id)
+            .filter(Technique.mitre_id.in_(mitre_ids))
+            .group_by(Technique.mitre_id)
+            .all()
+        )
+        for t in templates:
+            t.existing_test_count = counts.get(t.mitre_technique_id, 0)
+
     # Return templates
     return templates