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_coverage_by_tactic_order.py

@@ -0,0 +1,48 @@
+"""Tests for canonical MITRE kill-chain ordering in coverage-by-tactic.
+
+Block 3 fix: TacticCoverageChart.tsx (dashboard) rendered whatever order
+the backend happened to return (alphabetical, and only tactics with
+seeded techniques), while ExecutiveDashboardPage.tsx re-sorted client-side
+into the correct kill-chain order. get_coverage_by_tactic now returns the
+canonical order — and all 14 tactics, zero-filled — so both consumers get
+consistent results without needing their own reordering logic.
+"""
+
+from app.models.technique import Technique
+from app.services.metrics_query_service import MITRE_TACTIC_ORDER, get_coverage_by_tactic
+
+
+def test_coverage_by_tactic_returns_canonical_kill_chain_order(db):
+    # Seed a few tactics out of order to prove the response isn't alphabetical.
+    db.add(Technique(mitre_id="T3001", name="A", tactic="impact"))
+    db.add(Technique(mitre_id="T3002", name="B", tactic="execution"))
+    db.add(Technique(mitre_id="T3003", name="C", tactic="reconnaissance"))
+    db.commit()
+
+    rows = get_coverage_by_tactic(db)
+    tactics = [r.tactic for r in rows]
+
+    canonical_present = [t for t in tactics if t in MITRE_TACTIC_ORDER]
+    assert canonical_present == MITRE_TACTIC_ORDER
+
+
+def test_coverage_by_tactic_zero_fills_tactics_with_no_techniques(db):
+    db.add(Technique(mitre_id="T3004", name="D", tactic="execution"))
+    db.commit()
+
+    rows = get_coverage_by_tactic(db)
+    by_tactic = {r.tactic: r for r in rows}
+
+    assert "persistence" in by_tactic
+    assert by_tactic["persistence"].total == 0
+    assert by_tactic["execution"].total == 1
+
+
+def test_coverage_by_tactic_unknown_tactic_sorts_last(db):
+    db.add(Technique(mitre_id="T3005", name="E", tactic=None))
+    db.commit()
+
+    rows = get_coverage_by_tactic(db)
+    tactics = [r.tactic for r in rows]
+
+    assert tactics[-1] == "unknown"