feat(FN-3022): merge fusion/fn-3022

Commits merged:
- feat(FN-3022): complete Step 4 — document mobile quick chat autofocus behavior
- test(FN-3022): complete Step 2 — cover mobile autofocus and delayed enable path
- feat(FN-3022): complete Step 1 — reliable mobile autofocus when composer becomes ready

Files changed:
docs/dashboard-guide.md                            |  1 +
 packages/dashboard/app/components/QuickChatFAB.tsx | 42 +++++++++++++++---
 .../app/components/__tests__/QuickChatFAB.test.tsx | 51 ++++++++++++++++++++++
 3 files changed, 89 insertions(+), 5 deletions(-)

Fusion-Task-Id: FN-3022

docs/dashboard-guide.md

@@ -49,6 +49,7 @@ Quick Chat is an optional floating panel for fast, project-scoped assistant conv
 - `startFreshSession()` is the explicit new-thread action and always creates a new persisted session
 - Resume lookups use a targeted session query instead of loading the full active session list first
 - Tool-call summaries in the floating quick-chat panel are intentionally condensed into a single-line header row (especially on small screens) so tool name + status stay scannable without multi-line wrapping
+- On mobile viewports, opening Quick Chat auto-focuses the composer as soon as it is ready so the keyboard opens immediately
 
 ## Mailbox View