Add GitHub-like keyboard shortcuts for repository navigation:
- Press 'T' to focus the "Go to file" search input
- Press 'S' to focus the "Search code" input
- Press 'Escape' to blur focused search inputs
Both search inputs display a keyboard hint (kbd element) showing
the available shortcut. The hint hides when the input is focused
or has a value.
Includes unit tests and e2e tests for the new functionality.