docs(02-core-gameplay): create phase 2 plan

Two-wave plan for Core Gameplay phase: paddle2 + AI system (wave 1),
then game state machine + scoring + rendering (wave 2).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -60,7 +60,11 @@ Plans:
 5. Match ends when a player reaches target score with clear game-over state
 6. No memory leaks or event listener cleanup issues after multiple rounds
 
-**Plans**: TBD
+**Plans:** 2 plans
+
+Plans:
+- [ ] 02-01-PLAN.md — Paddle2, AI system (predictive interception + 3 difficulty levels), extended Input/Physics
+- [ ] 02-02-PLAN.md — Game state machine, scoring, match-end, re-serve, paddle2 rendering, mode/difficulty selection
 
 ---
 
@@ -138,7 +142,7 @@ Plans:
 | Phase | Plans Complete | Status | Completed |
 |-------|----------------|--------|-----------|
 | 1. Foundation | 1/2 | In Progress | — |
-| 2. Core Gameplay | 0/? | Not started | — |
+| 2. Core Gameplay | 0/2 | Not started | — |
 | 3. Complete Experience | 0/? | Not started | — |
 | 4. Polish & Depth | 0/? | Not started | — |
 | 5. Release | 0/? | Not started | — |
@@ -147,3 +151,4 @@ Plans:
 
 *Roadmap created: 2026-03-10*
 *Phase 1 planned: 2026-03-10*
+*Phase 2 planned: 2026-03-10*