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/metrics_query_service.py

@@ -38,6 +38,26 @@ from app.schemas.metrics import (
     ValidationRate,
 )
 
+# Canonical MITRE ATT&CK kill-chain order — used to sort "coverage by
+# tactic" consistently everywhere it's rendered (dashboard table, executive
+# bar chart), instead of each consumer inventing its own order/subset.
+MITRE_TACTIC_ORDER: list[str] = [
+    "reconnaissance",
+    "resource-development",
+    "initial-access",
+    "execution",
+    "persistence",
+    "privilege-escalation",
+    "defense-evasion",
+    "credential-access",
+    "discovery",
+    "lateral-movement",
+    "collection",
+    "command-and-control",
+    "exfiltration",
+    "impact",
+]
+
 
 # Define function get_coverage_summary
 def get_coverage_summary(db: Session) -> CoverageSummary:
@@ -112,6 +132,12 @@ def get_coverage_by_tactic(db: Session) -> list[TacticCoverage]:
         lambda: {s.value: 0 for s in TechniqueStatus}
     )
 
+    # Materialize every canonical tactic up front so the response always
+    # includes all 14, zero-filled, rather than only whichever tactics
+    # happen to have techniques seeded.
+    for tactic in MITRE_TACTIC_ORDER:
+        tactic_data[tactic]  # noqa: B018 — touch to create the defaultdict entry
+
     # Iterate over techniques
     for tactic_str, status in techniques:
         # Check: not tactic_str
@@ -128,10 +154,17 @@ def get_coverage_by_tactic(db: Session) -> list[TacticCoverage]:
             # Assign tactic_data[tactic][status.value] = 1
             tactic_data[tactic][status.value] += 1
 
+    def _tactic_sort_key(tactic: str) -> tuple[int, str]:
+        try:
+            return (MITRE_TACTIC_ORDER.index(tactic), tactic)
+        except ValueError:
+            # Anything outside the canonical 14 (e.g. "unknown") sorts last.
+            return (len(MITRE_TACTIC_ORDER), tactic)
+
     # Assign result = []
     result = []
     # Iterate over sorted(tactic_data)
-    for tactic in sorted(tactic_data):
+    for tactic in sorted(tactic_data, key=_tactic_sort_key):
         # Assign counts = tactic_data[tactic]
         counts = tactic_data[tactic]
         # Assign total = sum(counts.values())