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/checklists/requirements.md

@@ -0,0 +1,34 @@
+# Specification Quality Checklist: Header Navigation & Sign-Out Destination
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-05-03
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [X] No implementation details (languages, frameworks, APIs)
+- [X] Focused on user value and business needs
+- [X] Written for non-technical stakeholders
+- [X] All mandatory sections completed
+
+## Requirement Completeness
+
+- [X] No [NEEDS CLARIFICATION] markers remain
+- [X] Requirements are testable and unambiguous
+- [X] Success criteria are measurable
+- [X] Success criteria are technology-agnostic (no implementation details)
+- [X] All acceptance scenarios are defined
+- [X] Edge cases are identified
+- [X] Scope is clearly bounded
+- [X] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [X] All functional requirements have clear acceptance criteria
+- [X] User scenarios cover primary flows
+- [X] Feature meets measurable outcomes defined in Success Criteria
+- [X] No implementation details leak into specification
+
+## Notes
+
+- All items pass. Both changes are small, independent, and clearly bounded. Spec is ready for `/speckit-plan`.