feat(ui): make the sidebar brand link to Home

[Gordex2014]

Closes #552.

Summary

Makes the sidebar brand a native link to /ui, covering the logo, app name, and version. Because this is a regular <a href>, it preserves full-page browser navigation, keyboard activation, Ctrl/Cmd-click, and operation without JavaScript.

The logo remains decorative, while the link has a localized accessible name that remains available when the sidebar rail is collapsed. The existing Home navigation item remains the only element with aria-current="page".

Adds restrained hover and focus-visible affordances plus a no-JavaScript Playwright regression covering the native href, accessible name, decorative image, keyboard activation, and navigation to Home.

Testing

• HFS build with the UI enabled — passed
• git diff --check — passed
• cargo test -p helios-ui — 144 passed
• No-JavaScript Playwright suite — 9 passed
• WCAG 2.2 AA suite in light and dark themes — 20 passed
• Latest GitHub Actions: Test Rust, Linting, Security Audit, UI browser suite, Test Python, Test FHIRPath, Code Coverage, Codecov patch, and Cleanup Test Containers — passed

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Gordex2014]

Branch synchronization and CI follow-up:

• The PR branch now includes the latest main through cbae4a6b.
• The earlier JWKS 308 != 404 failure was an obsolete test inherited from the old base and was fixed by fix(rest,ui): unbreak main — drop rsa from JWKS derivation, fix the stale keys test #560.
• The later h2 security-audit failure was resolved by fix(ci): make leaked CI containers visible and reapable on the shared Docker host #563.
• The latest workflow runs are green, including Test Rust, the full helios-ui browser suite, linting, security audit, coverage, Python, and FHIRPath.
• The PR diff against main remains limited to the original three UI files for UI: make the sidebar logo link to the Home page #552.

The PR description has been updated with the current successful test results.