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/provider/repo/repo.go

@@ -203,13 +203,11 @@ func parallel(n int, f func(i int)) {
 	var wg sync.WaitGroup
 	sem := make(chan struct{}, max(8, runtime.NumCPU()))
 	for i := range n {
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
+		wg.Go(func() {
 			sem <- struct{}{}
 			defer func() { <-sem }()
 			f(i)
-		}()
+		})
 	}
 	wg.Wait()
 }