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/value.go

@@ -21,8 +21,6 @@ func NewSecretValue(b []byte) SecretValue {
 // Reveal returns the plaintext. Call it only to display or copy the value.
 func (v SecretValue) Reveal() string { return string(v.b) }
 
-func (v SecretValue) Len() int { return len(v.b) }
-
 func (v SecretValue) String() string   { return masked }
 func (v SecretValue) GoString() string { return masked }