fix: show search instead of grouped/flat in the Sources help bar (#6)

The Sources pane's help bar listed `` ` `` (grouped/flat sources), a rarely used toggle, but not Go to (`ctrl+s`), the main way to find things. Search now takes its place, right after `enter`; the toggle is still in `?`.

Golden output updated: at 100 columns the bar now reads `enter open • ctrl+s search • s copy link • S share… • f star • F favourites • … • ? help • q quit` (`n note` moves behind the `…`).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>
Reviewed-on: #6

internal/ui/app/help.go

@@ -46,7 +46,7 @@ func (c contextHelp) ShortHelp() []key.Binding {
 	}
 	switch c.focus {
 	case paneSources:
-		b = append(b, k.Enter, k.Share, k.ShareMenu, k.Favourite, k.Favourites, k.Note, k.SourcesView, k.Filter)
+		b = append(b, k.Enter, k.Search, k.Share, k.ShareMenu, k.Favourite, k.Favourites, k.Note, k.Filter)
 	case paneContainers:
 		b = append(b, k.Enter, k.Share, k.ShareMenu, k.Favourite, k.Note, k.Open, k.Filter)
 	default:

internal/ui/app/testdata/TestGolden.golden

@@ -27,4 +27,4 @@
 │                               ││                                                                 │
 │                               ││                                                                 │
 ╰────────────────────── 1 of 3 ─╯╰─────────────────────────────────────────────────────────────────╯
- enter open • s copy link • S share… • f star • F favourites • n note • … • ? help • q quit
+ enter open • ctrl+s search • s copy link • S share… • f star • F favourites • … • ? help • q quit