feat(FEAT-005): add contract assertion CRUD API endpoints

- Add GET /api/missions/milestones/:milestoneId/assertions
- Add POST /api/missions/milestones/:milestoneId/assertions
- Add GET /api/missions/assertions/:assertionId
- Add PATCH /api/missions/assertions/:assertionId
- Add DELETE /api/missions/assertions/:assertionId
- Add POST /api/missions/milestones/:milestoneId/assertions/reorder
- Add POST /api/missions/features/:featureId/assertions/:assertionId/link
- Add POST /api/missions/features/:featureId/assertions/:assertionId/unlink
- Add GET /api/missions/features/:featureId/assertions
- Add GET /api/missions/assertions/:assertionId/features
- Add GET /api/missions/milestones/:milestoneId/validation

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

packages/core/src/index.ts

@@ -181,6 +181,8 @@ export {
   SLICE_PLAN_STATES,
   FEATURE_LOOP_STATES,
   VALIDATOR_RUN_STATUSES,
+  MISSION_ASSERTION_STATUSES,
+  MILESTONE_VALIDATION_STATES,
 } from "./mission-types.js";
 export type {
   MissionStatus,
@@ -223,8 +225,6 @@ export type {
   MissionFixFeatureLineage,
   MissionFeatureLoopSnapshot,
   // Contract assertion types
-  MISSION_ASSERTION_STATUSES,
-  MILESTONE_VALIDATION_STATES,
   MissionAssertionStatus,
   MilestoneValidationState,
   MissionContractAssertion,