docs(03-01): complete PostgreSQL store and migration infrastructure plan

- Add 03-01-SUMMARY.md with full execution record
- Update STATE.md: advance to plan 2, record metrics and decisions
- Update ROADMAP.md: phase 03 in progress (1/2 plans complete)
- Update REQUIREMENTS.md: mark DB-01 and DB-03 complete

.planning/STATE.md

@@ -2,14 +2,14 @@
 gsd_state_version: 1.0
 milestone: v1.0
 milestone_name: milestone
-status: Ready to plan
-stopped_at: Phase 3 context gathered
-last_updated: "2026-03-24T07:46:57.289Z"
+status: Ready to execute
+stopped_at: Completed 03-01-PLAN.md
+last_updated: "2026-03-24T08:10:37.889Z"
 progress:
   total_phases: 4
   completed_phases: 2
-  total_plans: 4
-  completed_plans: 4
+  total_plans: 6
+  completed_plans: 5
 ---
 
 # Project State
@@ -19,12 +19,12 @@ progress:
 See: .planning/PROJECT.md (updated 2026-03-23)
 
 **Core value:** Reliable, persistent visibility into which services need updating — data never disappears, and the dashboard is the one place you trust to show the full picture.
-**Current focus:** Phase 02 — backend-refactor
+**Current focus:** Phase 03 — postgresql-support
 
 ## Current Position
 
-Phase: 3
-Plan: Not started
+Phase: 03 (postgresql-support) — EXECUTING
+Plan: 2 of 2
 
 ## Performance Metrics
 
@@ -50,6 +50,7 @@ Plan: Not started
 | Phase 01-data-integrity P02 | 7 | 2 tasks | 2 files |
 | Phase 02-backend-refactor P01 | 7min | 2 tasks | 7 files |
 | Phase 02-backend-refactor P02 | 3min | 2 tasks | 4 files |
+| Phase 03-postgresql-support P01 | 3min | 2 tasks | 7 files |
 
 ## Accumulated Context
 
@@ -70,6 +71,8 @@ Recent decisions affecting current work:
 - [Phase 02-backend-refactor]: golang-migrate v4.19.1 database/sqlite sub-package confirmed to use modernc.org/sqlite (no CGO); single 0001 baseline migration uses CREATE TABLE IF NOT EXISTS for backward compatibility
 - [Phase 02-backend-refactor]: Option B for test store access: internal helpers in export_test.go (TestUpsertEvent, TestGetUpdatesMap) instead of exported Store() accessor - keeps store field unexported
 - [Phase 02-backend-refactor]: NewTestServer pattern: each test gets its own in-memory SQLite DB (RunMigrations + NewSQLiteStore + NewServer) - eliminates shared global state between tests
+- [Phase 03-postgresql-support]: PostgresStore uses *sql.DB via pgx/v5/stdlib adapter with no mutex; TEXT timestamps match SQLiteStore scan logic
+- [Phase 03-postgresql-support]: CreateTag uses RETURNING id in PostgresStore (pgx does not support LastInsertId); AssignTag uses ON CONFLICT DO UPDATE
 
 ### Pending Todos
 
@@ -82,6 +85,6 @@ None yet.
 
 ## Session Continuity
 
-Last session: 2026-03-24T07:46:57.286Z
-Stopped at: Phase 3 context gathered
-Resume file: .planning/phases/03-postgresql-support/03-CONTEXT.md
+Last session: 2026-03-24T08:10:37.887Z
+Stopped at: Completed 03-01-PLAN.md
+Resume file: None