docs(03): create phase plan for Module System & Domaincheck

4 plans across 3 waves: SDK + registry (W1), Domaincheck module +
lazy loading (W2), visual verification (W3). Covers MOD-01..04,
DCHK-01..03.

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

.planning/ROADMAP.md

@@ -99,7 +99,20 @@ Decimal phases appear between their surrounding integers in numeric order.
   3. Module UIs load on demand (lazy loading) -- no bundle bloat from inactive modules
   4. User can open the Domaincheck module, enter a domain, and see whether it is registered or available
 
-**Plans**: TBD
+**Plans**: 4 plans
+
+**Wave 1**
+
+- [ ] 03-01-PLAN.md -- Module SDK, Prisma Registry, Activation API
+
+**Wave 2** *(blocked on Wave 1 completion)*
+
+- [ ] 03-02-PLAN.md -- Domaincheck Module: Backend DNS + Frontend UI
+- [ ] 03-03-PLAN.md -- Lazy Loading, Category Pages, Expanded Module View
+
+**Wave 3** *(blocked on Wave 2 completion)*
+
+- [ ] 03-04-PLAN.md -- Visual Verification: Human confirms module system
 **UI hint**: yes
 
 ### Phase 4: Marketplace & Portal Navigation
@@ -159,7 +172,7 @@ Phases execute in numeric order: 1 -> 2 -> 3 -> 4 -> 5 -> 6
 |-------|----------------|--------|-----------|
 | 1. Foundation & Portal Shell | 2/3 | In Progress | - |
 | 2. Authentication & Multi-Tenancy | 2/5 | In Progress|  |
-| 3. Module System & Domaincheck | 0/TBD | Not started | - |
+| 3. Module System & Domaincheck | 0/4 | Not started | - |
 | 4. Marketplace & Portal Navigation | 0/TBD | Not started | - |
 | 5. Dashboard & Calendar | 0/TBD | Not started | - |
 | 6. Desktop Client & CI/CD | 0/TBD | Not started | - |