Add plan format validator hook to detect malformed task labels

- Strengthen Prometheus plan template with FORMAT constraint
- Add task label format check to Oracle phase-2 (N/6 → N/7)
- Add format checks to self-review checklist
- New plan-format-validator hook: compares raw checkbox count
  against getPlanProgress() after plan writes, warns agent when
  labels are malformed (0/0 or partial skip scenarios)

src/config/schema/hooks.ts

@@ -57,6 +57,7 @@ export const HookNameSchema = z.enum([
   "todo-description-override",
   "webfetch-redirect-guard",
   "fsync-skip-warning",
+  "plan-format-validator",
   "legacy-plugin-toast",
 ])