Add back navigation link to /app on settings page

- Added ChevronLeft icon from lucide-react
- Added Link import from next/link
- Created back navigation component at top of settings page with hover state
- Links back to /app with "← Back" text

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

openspec/changes/user-accounts/tasks.md

@@ -71,7 +71,7 @@
 - [x] 12.1 `[sonnet]` Create `src/app/app/settings/page.tsx` — Profile section: display name input with save, read-only email
 - [x] 12.2 `[sonnet]` Add Security section: change password form (current/new/confirm) for credentials users, "Signed in via Google" for OAuth users
 - [x] 12.3 `[sonnet]` Add Danger Zone section: delete account button with confirmation dialog (type "DELETE" to confirm)
-- [ ] 12.4 `[haiku]` Add back navigation link to `/app`
+- [x] 12.4 `[haiku]` Add back navigation link to `/app`
 
 ## 13. App Layout & User Menu
 

src/app/app/settings/page.tsx

@@ -14,7 +14,8 @@ import {
   DialogHeader,
   DialogTitle,
 } from "@/components/ui/dialog";
-import { CheckCircle, AlertCircle, Trash2 } from "lucide-react";
+import { CheckCircle, AlertCircle, Trash2, ChevronLeft } from "lucide-react";
+import Link from "next/link";
 
 export default function SettingsPage() {
   const { data: session, update } = useSession();
@@ -159,6 +160,12 @@ export default function SettingsPage() {
 
   return (
     <div className="max-w-xl mx-auto py-10 px-4 space-y-6">
+      <div className="flex items-center gap-2">
+        <Link href="/app" className="inline-flex items-center gap-1 text-muted-foreground hover:text-foreground transition-colors">
+          <ChevronLeft className="h-4 w-4" />
+          <span className="text-sm font-mono">Back</span>
+        </Link>
+      </div>
       <h1 className="text-2xl font-bold font-mono tracking-tight">Settings</h1>
 
       {/* Profile section */}