docs(15-01): complete Logto Docker infrastructure plan

- Create 15-01-SUMMARY.md with execution results
- Update STATE.md with phase 15 position and decisions
- Update ROADMAP.md with plan progress
- Mark AUTH-04 requirement complete

.planning/STATE.md

@@ -25,19 +25,19 @@ See: .planning/PROJECT.md (updated 2026-04-03)
 
 ## Current Position
 
-Phase: 14 of 18 (PostgreSQL Migration)
-Plan: 0 of ? in current phase
-Status: Ready to plan
-Last activity: 2026-04-03 — v2.0 roadmap created (Phases 14-18)
+Phase: 15 of 18 (External Authentication)
+Plan: 1 of 3 in current phase
+Status: Executing
+Last activity: 2026-04-04 — Completed 15-01 (Logto Docker infrastructure + schema cleanup)
 
-Progress: [----------] 0% (v2.0 milestone)
+Progress: [=---------] 5% (v2.0 milestone)
 
 ## Performance Metrics
 
 **Velocity:**
-- Total plans completed: 0 (v2.0 milestone)
-- Average duration: --
-- Total execution time: --
+- Total plans completed: 1 (v2.0 milestone)
+- Average duration: 3min
+- Total execution time: 3min
 
 *Updated after each plan completion*
 
@@ -45,13 +45,15 @@ Progress: [----------] 0% (v2.0 milestone)
 
 ### Decisions
 
-Key decisions made during v2.0 planning:
+Key decisions made during v2.0 planning and execution:
 - Platform pivot: single-user to multi-user with discovery-first approach
-- External auth provider (self-hosted, open-source) — Logto vs Authentik OPEN decision
+- External auth provider (self-hosted, open-source) — Logto selected (D-01)
 - SQLite to Postgres migration — required by auth provider and multi-user concurrency
 - Structured UGC only — ratings and predefined fields, no freeform text until moderation
 - Separate globalItems table — not a flag on user items table
 - Single-user SQLite mode diverges at v2.0 boundary
+- Logto shares Postgres instance via separate database created by init script
+- OIDC_ISSUER derived from LOGTO_ENDPOINT in docker-compose
 
 ### Pending Todos
 
@@ -64,6 +66,6 @@ None active.
 
 ## Session Continuity
 
-Last session: 2026-04-03
-Stopped at: v2.0 roadmap created with 5 phases (14-18) covering 30 requirements
+Last session: 2026-04-04
+Stopped at: Completed 15-01-PLAN.md (Logto Docker infrastructure + schema cleanup)
 Resume file: None