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

docs/architecture.md

@@ -160,8 +160,17 @@ The roadmap model is intentionally lightweight and independent from `MissionStor
 - FK cascade integrity: deleting a roadmap removes milestones and features
 - Export/handoff DTO methods for integration with downstream systems:
   - `getRoadmapExport()` → `RoadmapExportBundle` (flat export payload)
-  - `getRoadmapMissionHandoff()` → `RoadmapMissionPlanningHandoff` (mission conversion)
-  - `getRoadmapFeatureHandoff()` → `RoadmapFeatureTaskPlanningHandoff` (task planning)
+  - `getMissionPlanningHandoff()` → `RoadmapMissionPlanningHandoff` (mission conversion)
+  - `listFeatureTaskPlanningHandoffs()` → `RoadmapFeatureTaskPlanningHandoff[]` (all features as task handoffs)
+  - `getRoadmapFeatureHandoff()` → `RoadmapFeatureTaskPlanningHandoff` (single feature task handoff)
+- Pure handoff mapping helpers in `roadmap-handoff.ts` for read-only transformations
+
+**Roadmap handoff contract boundary (FN-1674):**
+- Handoffs are **read-only** transformations — no mission/task records are created
+- Source lineage is preserved on every emitted item (roadmapId, milestoneId, featureId, titles, order indices)
+- Ordering is deterministic using `normalizeRoadmapMilestoneOrder` and `normalizeRoadmapFeatureOrder`
+- Not-found semantics: store handoff methods throw when roadmapId is unknown; routes map to HTTP 404
+- The combined handoff endpoint (`GET /:roadmapId/handoff`) returns both mission and task handoffs
 
 Key roadmap invariants:
 - milestone ordering is scoped to a single roadmap and must remain contiguous + 0-based
@@ -173,7 +182,7 @@ Key roadmap invariants:
 - Roadmaps: `GET /`, `POST /`, `GET /:roadmapId`, `PATCH /:roadmapId`, `DELETE /:roadmapId`
 - Milestones: `GET /:roadmapId/milestones`, `POST /:roadmapId/milestones`, `PATCH /milestones/:milestoneId`, `DELETE /milestones/:milestoneId`, `POST /:roadmapId/milestones/reorder`
 - Features: `GET /milestones/:milestoneId/features`, `POST /milestones/:milestoneId/features`, `PATCH /features/:featureId`, `DELETE /features/:featureId`, `POST /milestones/:milestoneId/features/reorder`, `POST /features/:featureId/move`
-- Export/Handoff: `GET /:roadmapId/export`, `GET /:roadmapId/handoff/mission`, `GET /:roadmapId/milestones/:milestoneId/features/:featureId/handoff/task`
+- Export/Handoff: `GET /:roadmapId/export`, `GET /:roadmapId/handoff`, `GET /:roadmapId/handoff/mission`, `GET /:roadmapId/milestones/:milestoneId/features/:featureId/handoff/task`
 
 **Database schema:**
 - `roadmaps` — roadmap metadata (id, title, description, timestamps)

docs/dashboard-guide.md

@@ -295,6 +295,33 @@ Within each milestone, you can generate AI-powered feature suggestions to quickl
 - **No milestones**: "This roadmap has no milestones. Click + on a milestone lane to add one."
 - **No features**: "No features yet." displayed within each milestone card
 
+### Roadmap Export / Handoff
+
+Roadmaps can be exported as structured data for use in mission and task planning flows.
+
+**How to use:**
+
+1. Hover over a roadmap in the sidebar
+2. Click the **download icon** (↘) to open the export modal
+3. Click **Load Handoff Data** to fetch the roadmap's handoff payload
+4. Review the exported data:
+   - **Mission Planning Handoff**: Roadmap structure with milestones and features in deterministic order
+   - **Feature Task Handoffs**: Individual feature entries with source lineage (roadmap ID, milestone ID, feature ID, titles, and order indices)
+
+**Key features:**
+
+- This is a **read-only** export — no missions, slices, or tasks are created
+- The handoff preserves source lineage for traceability to the original roadmap
+- Ordering is deterministic (milestone order, then feature order)
+- Click **Copy to Clipboard** to copy the full handoff payload as JSON
+- Handoff data can be manually used to seed mission planning prompts or task creation flows
+
+**Use cases:**
+
+- Export a roadmap's milestone/feature structure to guide AI-assisted mission planning
+- Copy individual feature handoffs as task planning prompts
+- Preserve roadmap context when creating tasks in the task board
+
 ## Task Detail Modal
 
 Inspect logs, step progress, workflow outcomes, and model overrides.