FN-5682: render mission markdown across manager views

Render mission, milestone, slice, and feature text as Markdown in MissionManager.

- add a shared markdown renderer using react-markdown with GFM support
- render mission descriptions, milestone acceptance criteria, slice verification, and feature description/acceptance fields as markdown
- render feature-derived completion criteria and mission list descriptions as markdown
- add MissionManager markdown styling and update mission docs/tests for markdown behavior

Files changed:
 docs/missions.md                                   |  2 +
 .../dashboard/app/components/MissionManager.css    | 45 ++++++++++++
 .../dashboard/app/components/MissionManager.tsx    | 46 ++++++++----
 .../components/__tests__/MissionManager.test.tsx   | 85 ++++++++++++++++++----
 4 files changed, 146 insertions(+), 32 deletions(-)

Fusion-Task-Id: FN-5682

Fusion-Task-Lineage: 521193fb-7150-44ab-981f-045c094f32df

docs/missions.md

@@ -42,6 +42,8 @@ On mobile, Mission Manager surfaces the primary **Plan New Mission** CTA at the
 
 Mission detail refreshes now preserve expanded milestone/slice state and keep the selected milestone expanded, so persisted milestone acceptance criteria remain visible across live updates.
 
+Mission, milestone, slice, and feature read-only text surfaces in Mission Manager render Markdown (GFM) for descriptions, verification, and acceptance criteria; edit forms continue to use raw plain-text `<textarea>` inputs.
+
 ### CLI
 
 ```bash