docs(03-postgresql-support): create phase plan

.planning/ROADMAP.md

@@ -58,8 +58,11 @@ Plans:
   2. A fresh PostgreSQL deployment receives all schema tables via automatic migration on startup
   3. An existing SQLite user can upgrade to the new binary without any data loss or manual schema changes
   4. The app can be run with Docker Compose using an optional postgres service profile
-**Plans**: TBD
-**UI hint**: no
+**Plans**: 2 plans
+
+Plans:
+- [ ] 03-01-PLAN.md — Create PostgresStore (9 Store methods), PostgreSQL migration files, rename RunMigrations to RunSQLiteMigrations, add RunPostgresMigrations
+- [ ] 03-02-PLAN.md — Wire DATABASE_URL branching in main.go, fix cross-dialect UNIQUE detection, add Docker Compose postgres profiles, create build-tagged test helper
 
 ### Phase 4: UX Improvements
 **Goal**: Users can manage a large list of updates efficiently — dismissing many at once, finding specific images quickly, and seeing new arrivals without manual refreshes
@@ -84,5 +87,5 @@ Phases execute in numeric order: 1 → 2 → 3 → 4
 |-------|----------------|--------|-----------|
 | 1. Data Integrity | 0/2 | Not started | - |
 | 2. Backend Refactor | 2/2 | Complete   | 2026-03-24 |
-| 3. PostgreSQL Support | 0/? | Not started | - |
+| 3. PostgreSQL Support | 0/2 | Not started | - |
 | 4. UX Improvements | 0/? | Not started | - |