feat(FN-4123): restore latest quick chat session on startup

Restores the most recent quick chat session when the FAB is reopened, eliminating the need to navigate to the full chat view to continue a conversation. The feature lives in `QuickChatFAB.tsx` with corresponding tests, and includes documentation and a changeset for the `@runfusion/fusion` patch rele

Fusion-Task-Id: FN-4123

docs/dashboard-guide.md

@@ -138,6 +138,7 @@ Quick Chat is an optional floating panel for fast, project-scoped assistant conv
 - Entering `/new` or `/clear` (exact match after trimming) in the Quick Chat composer uses explicit fresh-session creation for the currently selected target (`startFreshSession()`), so the current thread resets without sending the command text to the model
 - The `+` action opens an inline new-session chooser (inside the panel, not a modal) with `Model` selected by default and optional switch to `Agent`
 - Submitting the inline chooser uses explicit fresh-session creation and immediately persists/selects the new thread, then refreshes the session dropdown list
+- On open after reload, Quick Chat restores the most recently used session (newest `updatedAt`); only when no prior session exists does it fall back to the first agent / configured default model.
 - Resume lookups still use targeted session queries 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