Feat: Header title links to grid; sign-out redirects to grid

Make the app title a clickable link to / so users can return to the
image grid from any sub-page without the browser back button. Change
the sign-out destination from /login to / since the grid is publicly
accessible and avoids unnecessary friction post-logout.

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

specs/006-header-nav-signout/plan.md

@@ -0,0 +1,25 @@
+# Implementation Plan: Header Navigation & Sign-Out Destination
+
+**Branch**: `006-header-nav-signout` | **Date**: 2026-05-03 | **Spec**: [spec.md](spec.md)
+
+## Summary
+
+Two targeted changes to `ui/src/app/app.component.ts`:
+1. Wrap the header app-name text in a router link to `/`.
+2. Change the post-sign-out navigation target from `/login` to `/`.
+
+No API changes. No new dependencies. One component file affected.
+
+## Technical Context
+
+**Language/Version**: TypeScript 5 / Angular 19 (standalone components)
+**Affected files**: `ui/src/app/app.component.ts`, `ui/src/app/app.component.spec.ts`
+**Testing**: Karma / Jasmine
+
+## Constitution Check
+
+| Principle | Status |
+|-----------|--------|
+| §2.1 Strict separation of concerns | ✅ UI-only change |
+| §5.1 TDD non-negotiable | ✅ Tests written first |
+| §7.3 Linting non-optional | ✅ ng lint gate in tasks |