feat(FN-787): replace project-switch icon with Building2 for visual distinction

- Replace Folder icon with Building2 in Header project-switch overflow button
- Add Header test for distinct project-switch icon rendering
- Update dashboard README docs for responsive header icon change

packages/dashboard/app/components/Header.tsx

@@ -1,5 +1,5 @@
 import { useState, useEffect, useRef, useCallback } from "react";
-import { Settings, Pause, Play, Square, LayoutGrid, List, Terminal, Lightbulb, Search, X, Activity, MoreHorizontal, Clock, Folder, History, GitBranch, Workflow, Bot, ChevronLeft, Target } from "lucide-react";
+import { Settings, Pause, Play, Square, LayoutGrid, List, Terminal, Lightbulb, Search, X, Activity, MoreHorizontal, Clock, Folder, History, GitBranch, Workflow, Bot, ChevronLeft, Target, Building2 } from "lucide-react";
 import type { ProjectInfo } from "../api";
 import { ProjectSelector } from "./ProjectSelector";
 import { QuickScriptsDropdown } from "./QuickScriptsDropdown";
@@ -490,7 +490,7 @@ export function Header({
                 role="menuitem"
                 data-testid="overflow-project-selector-btn"
               >
-                <Folder size={16} />
+                <Building2 size={16} />
                 <span>{currentProject ? currentProject.name : "Switch Project"}</span>
               </button>
             )}