feat(shortcut): Add keyboard shortcuts for repository file and code search

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.

templates/repo/home_sidebar_top.tmpl

@@ -1,7 +1,9 @@
 <div class="repo-home-sidebar-top">
 	<form class="ignore-dirty tw-flex tw-flex-1" action="{{.RepoLink}}/search" method="get">
-		<div class="ui small action input tw-flex-1">
-			<input name="q" size="10" placeholder="{{ctx.Locale.Tr "search.code_kind"}}"> {{template "shared/search/button"}}
+		<div class="ui small action input tw-flex-1 repo-code-search-input-wrapper">
+			<input name="q" size="10" placeholder="{{ctx.Locale.Tr "search.code_kind"}}" class="code-search-input">
+			<kbd class="repo-search-shortcut-hint">S</kbd>
+			{{template "shared/search/button"}}
 		</div>
 	</form>