feat(FN-1690): add RoadmapStore with SQLite persistence

- Implement RoadmapStore with CRUD operations for roadmaps, milestones, and features
- Add roadmap schema migration v32 with roadmaps, roadmap_milestones, and roadmap_features tables
- Add covering indexes for deterministic ordering within roadmaps and milestones
- Wire RoadmapStore access via TaskStore.getRoadmapStore()
- Update architecture.md documentation with RoadmapStore persistence
- Add comprehensive tests for RoadmapStore CRUD and ordering
- Update db.test.ts with schema v32 assertions
- Add UpdateInput type imports to task-documents.test.ts
- Export RoadmapStore from core index.ts

packages/core/src/__tests__/task-documents.test.ts

@@ -51,7 +51,7 @@ describe("TaskStore task documents", () => {
 
     expect(tableNames.has("task_documents")).toBe(true);
     expect(tableNames.has("task_document_revisions")).toBe(true);
-    expect(db.getSchemaVersion()).toBe(31);
+    expect(db.getSchemaVersion()).toBe(32);
 
     const index = db
       .prepare(