feat(KB-636): launch missions feature

- Add MissionStore integration tests for core mission operations

- Add mission API end-to-end tests for dashboard endpoints

- Add Missions documentation to README with usage examples

- Update CLI help text with mission commands

- Add changeset for missions package release

.changeset/missions-launch.md

@@ -0,0 +1,23 @@
+---
+"@gsxdsm/fusion": minor
+---
+
+Add Missions system for large-scale project planning.
+
+The Missions system provides a hierarchical planning structure:
+- **Mission** — High-level goals and projects
+- **Milestone** — Major phases within missions  
+- **Slice** — Parallel work areas within milestones
+- **Feature** — Individual deliverables linked to tasks
+
+**New Features:**
+- SQLite database schema for mission hierarchy with automatic status rollup
+- MissionStore with full CRUD operations and event emissions
+- REST API endpoints for mission, milestone, slice, and feature management
+- CLI commands: `fn mission create`, `list`, `show`, `delete`, `activate-slice`
+- Dashboard UI components for mission management
+
+**Usage:**
+- Create missions with `fn mission create "Title" "Description"`
+- View hierarchy with `fn mission show <id>`
+- Link features to tasks for automatic progress tracking