feat(FN-1674): add roadmap export and handoff system

- Add RoadmapStore with read APIs for project-scoped roadmap data
- Add roadmap-handoff mapper to transform roadmap data for export
- Add project-scoped handoff API route (/api/projects/:id/roadmap/handoff)
- Add useRoadmaps hook for fetching and exposing roadmap data to components
- Update RoadmapsView with export/handoff UX path and roadmap detail view
- Add roadmap routes with project-scoped handoff endpoint
- Add comprehensive tests for handoff mapper and roadmap routes
- Update architecture.md and add dashboard-guide.md documentation

packages/core/src/index.ts

@@ -200,6 +200,12 @@ export {
   applyRoadmapFeatureReorder,
   moveRoadmapFeature,
 } from "./roadmap-ordering.js";
+export {
+  mapFeatureToTaskHandoff,
+  mapRoadmapToMissionHandoff,
+  mapRoadmapWithHierarchyToMissionHandoff,
+  mapAllFeaturesToTaskHandoffs,
+} from "./roadmap-handoff.js";
 
 // ── Mission Hierarchy Types ────────────────────────────────────────────