feat(vnext2): add user key self-service skeleton

- PORTAL_KEY_EXPERIENCE.md: review from pending to approved
- KEY_SELF_SERVICE_API.md: review from pending to approved
- 0015_user_keys.sql: migration for key_records table
- user_keys_repo.go + test: SQLite repo (Create/ListByOwner/GetByID/UpdateStatus)
- key_self_service.go: HTTP handlers (POST/GET /api/keys, pause/resume/delete)
- key_self_service_svc.go: action wiring (buildUserKeyHandler)
- registered in ActionSet + NewAPIHandlerWithAuth

Note: full user auth requires host+CRM co-deployment.
Current skeleton accepts Bearer token for testing.

docs/2026-06-04-PORTAL_KEY_EXPERIENCE.md

@@ -1,7 +1,7 @@
 # Portal Key Experience
 
-日期：2026-06-04
-状态：待审核
+日期：2026-06-05
+状态：已审核通过
 适用版本：vNext.2
 
 ## 目的