docs(specs): mark auth-unification-migration complete

All spec deliverables shipped:

- pkg bumped v0.13.0 -> v0.17.1
- Adopted authkit.DeviceCodeClient in runDeviceFlow (captureStore
  bridges to api.Token storage for compatibility with latere lux)
- 'latere auth org switch' subcommand drives the refresh-grant
  org-switch contract documented in auth/specs/refresh-token-org-switch.md
- --personal flag and empty-string id both switch to personal context

Author: changkun

specs/auth-unification-migration.md

@@ -1,6 +1,6 @@
 ---
 title: latere-cli — Auth Unification Migration
-status: in-progress
+status: complete
 depends_on:
   - "auth/specs/auth-unification.md"
   - "auth/specs/auth-unification/authkit-device-code-and-token-store.md"