chore(xce-harness-component): mark spec implementation-complete

All 16 tasks implemented, independently reviewed, and feature-level
validated GO (/kiro-validate-impl): mechanical (173+1213 tests, 0
failures), design/boundary alignment (zero controller-private
dependency, both sanctioned exceptions exact match), requirements
coverage (22/22 mapped), and all four downstream workflows verified
end-to-end from a genuinely harness-absent build state.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLSNJhNoULvVcUhXEFafQC

.kiro/specs/xce-harness-component/spec.json

@@ -1,9 +1,9 @@
 {
   "feature_name": "xce-harness-component",
   "created_at": "2026-09-14T02:46:14Z",
-  "updated_at": "2026-09-14T03:35:00Z",
+  "updated_at": "2026-09-14T10:50:00Z",
   "language": "en",
-  "phase": "tasks-generated",
+  "phase": "implementation-complete",
   "approvals": {
     "requirements": {
       "generated": true,