docs(15-02): complete OIDC auth integration plan

- Add 15-02-SUMMARY.md with execution results
- Update STATE.md with position, decisions, session info
- Update ROADMAP.md with plan progress
- Mark AUTH-01, AUTH-02, AUTH-03 requirements complete

.planning/ROADMAP.md

@@ -51,7 +51,7 @@
 **Milestone Goal:** Transform GearBox from a single-user gear tracker into a multi-user platform where people discover gear, research purchases using crowd-verified data, and share their setups.
 
 - [ ] **Phase 14: PostgreSQL Migration** — Replace SQLite with Postgres, make all operations async, establish new test infrastructure
-- [ ] **Phase 15: External Authentication** — Integrate self-hosted OIDC auth provider for user registration and login
+- [x] **Phase 15: External Authentication** — Integrate self-hosted OIDC auth provider for user registration and login (completed 2026-04-04)
 - [ ] **Phase 16: Multi-User Data Model** — Add user ownership to all entities with cross-user data isolation
 - [ ] **Phase 17: Object Storage** — Move images from local filesystem to MinIO (S3-compatible)
 - [ ] **Phase 18: Global Items & Public Profiles** — Global item catalog, user profiles, and public setup sharing
@@ -189,7 +189,7 @@ Plans:
 | 12. Comparison View | v1.3 | 1/1 | Complete | 2026-03-17 |
 | 13. Setup Impact Preview | v1.3 | 0/2 | Not started | - |
 | 14. PostgreSQL Migration | v2.0 | 0/? | Not started | - |
-| 15. External Authentication | v2.0 | 0/? | Not started | - |
+| 15. External Authentication | v2.0 | 2/1 | Complete   | 2026-04-04 |
 | 16. Multi-User Data Model | v2.0 | 0/? | Not started | - |
 | 17. Object Storage | v2.0 | 0/? | Not started | - |
 | 18. Global Items & Public Profiles | v2.0 | 0/? | Not started | - |