feat(FN-2188): harden dev server view lifecycle and mobile nav

- Update the dashboard dev-server API client for compatibility with multiple backend response shapes
- Refine useDevServer polling and SSE lifecycle handling to improve status/action reliability
- Gate dev server navigation in header/mobile overflow and fix mobile preview header wrapping styles
- Expand DevServerView and useDevServer test coverage with isolated mocks and log/status assertions
- Document the devServerView experimental feature flag in settings reference

docs/settings-reference.md

@@ -384,6 +384,14 @@ The Experimental Features section in Settings shows:
 - Project scope indicator (features are project-specific, not global)
 - Description explaining the purpose of experimental features
 
+Common built-in dashboard flags include:
+- `insights`
+- `roadmap`
+- `memoryView`
+- `skillsView`
+- `nodesView`
+- `devServerView`
+
 ---
 
 ## Background Memory Summarization & Audit