fix(FN-1488): add showQuickChatFAB setting to control Quick Chat FAB visibility

- Add showQuickChatFAB boolean setting to ProjectSettings type
- Add useAppSettings hook function for accessing the setting
- Wire QuickChatFAB visibility in App.tsx based on setting
- Hide QuickChatFAB in MobileNavBar when setting is false
- Add Settings UI toggle for the new setting
- Add CSS for hiding QuickChatFAB on mobile when disabled
- Add comprehensive tests for all affected components
- Fix QuickChatFAB onOpenChange test to use controlled mode
- Update settings reference documentation

packages/core/src/__tests__/settings-parity.test.ts

@@ -99,6 +99,7 @@ const PROJECT_KEYS: (keyof ProjectSettings)[] = [
   "reflectionIntervalMs",
   "reflectionAfterTask",
   "reviewHandoffPolicy",
+  "showQuickChatFAB",
 ];
 
 function assertExactKeyCoverage(scopeName: string, actual: readonly string[], expected: readonly string[]): void {

packages/core/src/types.ts

@@ -1144,6 +1144,10 @@ export interface ProjectSettings {
    *  - "always": Always handoff after completion (not implemented, reserved for future)
    */
   reviewHandoffPolicy?: "disabled" | "comment-triggered" | "always";
+  /** When true, show the quick-chat floating action button (FAB) in the dashboard.
+   *  When false, the FAB is hidden but chat remains accessible via the More menu.
+   *  Default: true. */
+  showQuickChatFAB?: boolean;
 }
 
 /**
@@ -1255,6 +1259,7 @@ export const DEFAULT_PROJECT_SETTINGS: ProjectSettings = {
   reflectionIntervalMs: 3_600_000,
   reflectionAfterTask: true,
   reviewHandoffPolicy: "disabled",
+  showQuickChatFAB: true,
 };
 
 /**
@@ -1361,6 +1366,7 @@ export const PROJECT_SETTINGS_KEYS: ReadonlyArray<keyof ProjectSettings> = [
   "reflectionIntervalMs",
   "reflectionAfterTask",
   "reviewHandoffPolicy",
+  "showQuickChatFAB",
 ] as const;
 
 // ── Compile-time parity: ensures every interface key is listed exactly once ──