refactor: merge QuickLaunch into CommandPalette, amber New Session button

- Remove QuickLaunch (lightning bolt) from TopBar — redundant with CommandPalette
- Delete QuickLaunch.tsx (dead code, no remaining imports)
- Add "New Project" to CommandPalette quick actions
- Change sidebar "New Session" button from cyan to amber-400

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -367,7 +367,7 @@ export function Sidebar() {
         <div className="px-3 pt-3 pb-1">
           <Link
             to="/"
-            className="flex items-center justify-center gap-2 w-full rounded-lg bg-primary/15 py-2.5 text-sm font-semibold text-primary hover:bg-primary/25 transition-colors"
+            className="flex items-center justify-center gap-2 w-full rounded-lg bg-amber-400/15 py-2.5 text-sm font-semibold text-amber-400 hover:bg-amber-400/25 transition-colors"
           >
             <Plus size={16} strokeWidth={2} />
             New Session
@@ -424,7 +424,7 @@ export function Sidebar() {
         <div className="w-full px-2 pt-4 pb-2">
           <Link
             to="/"
-            className="flex flex-col items-center justify-center w-full rounded-lg bg-primary/15 py-2.5 text-primary hover:bg-primary/25 transition-colors"
+            className="flex flex-col items-center justify-center w-full rounded-lg bg-amber-400/15 py-2.5 text-amber-400 hover:bg-amber-400/25 transition-colors"
             title="New Session"
           >
             <Plus size={20} strokeWidth={2} />