docs(02): create phase plan

Phase 02: Plugin System
- 3 plans in 3 waves (sequential)
- 02-01: Plugin discovery and manifest parsing
- 02-02: Lifecycle management and dependency resolution
- 02-03: Extension API with type-safe plugin-to-plugin communication
- Ready for execution

.planning/ROADMAP.md

@@ -52,12 +52,12 @@ Plans:
   3. Plugin lifecycle executes in correct order (register, boot, shutdown)
   4. Plugin dependencies resolve correctly (plugin A requiring plugin B loads B first)
   5. Plugin can extend another plugin via type-safe extension API
-**Plans**: TBD
+**Plans**: 3 plans
 
 Plans:
-- [ ] 02-01: Plugin discovery and manifest parsing
-- [ ] 02-02: Lifecycle management and dependency resolution
-- [ ] 02-03: Extension API with type-safe plugin-to-plugin communication
+- [ ] 02-01-PLAN.md - Plugin discovery and manifest parsing (circe-yaml, PluginId, PluginManifest, PluginDiscovery)
+- [ ] 02-02-PLAN.md - Lifecycle management and dependency resolution (SummerPlugin trait, PluginManager, topological sort)
+- [ ] 02-03-PLAN.md - Extension API with type-safe plugin-to-plugin communication (EventService, ExtensionRegistry)
 
 ### Phase 3: Component System
 **Goal**: Enable reusable UI components that respond to HTMX interactions
@@ -206,8 +206,8 @@ Phases execute in numeric order: 1 -> 2 -> 3 -> 4 -> 5 -> 6 -> 7 -> 8 -> 9 -> 10
 
 | Phase | Plans Complete | Status | Completed |
 |-------|----------------|--------|-----------|
-| 1. Foundation | 3/3 | ✓ Complete | 2026-02-05 |
-| 2. Plugin System | 0/3 | Not started | - |
+| 1. Foundation | 3/3 | Complete | 2026-02-05 |
+| 2. Plugin System | 0/3 | Planned | - |
 | 3. Component System | 0/2 | Not started | - |
 | 4. Theme Engine | 0/2 | Not started | - |
 | 5. CLI Scaffolding | 0/2 | Not started | - |