refactor: drop dead code and use the standard library where it already does the job

No behaviour change.

- Deleted, unused or one-line wrappers: panes.RuneIndexes, Detail.Refresh (SetDescribed does it), SecretValue.Len, Query.Empty, Clipboard.Native, config.Load, get's value, Model.done, providerOf (cachefile.ProviderOf), contextWithTimeout, searchCoverage, startCrawl, showKeybindings, the expiry aliases and daysLeft.
- cmp.Or instead of the two cmpOr copies; slices.Sorted(maps.Keys(…)), maps.Copy, wg.Go, utf8.RuneCountInString and new(true) instead of loops and helpers that do the same.
- A container's pane title is set once, not twice; a redundant length check in share links and a no-op assignment in linkhandler.Launch are gone.
- Tests call ansi.Strip and lastLines directly; gofmt -s on links.go.

internal/ui/app/app_test.go

@@ -991,11 +991,11 @@ func TestRebindingShowsEverywhere(t *testing.T) {
 	if !strings.Contains(scr, "z to reveal") || strings.Contains(scr, "space to reveal") {
 		t.Errorf("detail hint doesn't follow the binding:\n%s", scr)
 	}
-	if !strings.Contains(lastLine(scr), "z show") {
-		t.Errorf("help bar: %q", lastLine(scr))
+	if !strings.Contains(lastLines(scr, 1), "z show") {
+		t.Errorf("help bar: %q", lastLines(scr, 1))
 	}
 	d.keys("z")
-	if bar := lastLine(d.screen()); !strings.Contains(bar, "z hide") {
+	if bar := lastLines(d.screen(), 1); !strings.Contains(bar, "z hide") {
 		t.Errorf("help bar with the value shown: %q", bar)
 	}
 	d.keys("z")
@@ -1125,7 +1125,7 @@ func TestAccountPane(t *testing.T) {
 	if !strings.Contains(scr, "Alice Example") {
 		t.Errorf("account not shown:\n%s", scr)
 	}
-	bar := lastLine(scr)
+	bar := lastLines(scr, 1)
 	if !strings.Contains(bar, "copy") || strings.Contains(bar, "reveal") || strings.Contains(bar, "versions") {
 		t.Errorf("help bar: %q", bar)
 	}