docs(02.1): create phase plan for additional sports stadiums

Phase 2.1: Additional Sports Stadiums
- 3 plans created (MLS, WNBA, NWSL modules)
- CBB deferred to future phase (350+ D1 teams)
- 6 total tasks defined
- Ready for execution

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -46,13 +46,15 @@ Plans:
 - [x] 02-02: Regenerate canonical data and verify pipeline
 
 ### Phase 2.1: Additional Sports Stadiums (INSERTED)
-**Goal**: Add hardcoded stadium data for secondary sports: MLS, WNBA, NWSL, and CBB (College Basketball)
+**Goal**: Add hardcoded stadium data for secondary sports: MLS, WNBA, NWSL (CBB deferred - 350+ D1 teams requires separate scoped phase)
 **Depends on**: Phase 2
-**Research**: Unlikely (stadium data compilation)
-**Plans**: TBD
+**Research**: No (stadium data compilation following established patterns)
+**Plans**: 3 plans
 
 Plans:
-- [ ] 02.1-01: TBD (run /gsd:plan-phase 2.1 to break down)
+- [ ] 02.1-01: Create MLS module with 30 hardcoded stadiums
+- [ ] 02.1-02: Create WNBA module with 13 hardcoded arenas
+- [ ] 02.1-03: Create NWSL module with 13+ hardcoded stadiums
 
 ### Phase 3: Alias Systems
 **Goal**: Implement alias systems for both stadiums and teams to handle name variations across data sources
@@ -100,7 +102,7 @@ Phases execute in numeric order: 1 → 2 → 2.1 → 3 → 4 → 5 → 6
 |-------|----------------|--------|-----------|
 | 1. Script Architecture | 3/3 | Complete | 2026-01-10 |
 | 2. Stadium Foundation | 2/2 | Complete | 2026-01-10 |
-| 2.1. Additional Sports Stadiums | 0/TBD | Not started | - |
+| 2.1. Additional Sports Stadiums | 0/3 | Not started | - |
 | 3. Alias Systems | 0/TBD | Not started | - |
 | 4. Canonical Linking | 0/TBD | Not started | - |
 | 5. CloudKit CRUD | 0/TBD | Not started | - |