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/instance/instance.go

@@ -9,7 +9,6 @@
 package instance
 
 import (
-	"bufio"
 	"context"
 	"encoding/json"
 	"errors"
@@ -114,7 +113,7 @@ func (s *Server) handle(c net.Conn) {
 	defer c.Close()
 	_ = c.SetDeadline(time.Now().Add(5 * time.Second))
 	var req request
-	if err := json.NewDecoder(bufio.NewReader(c)).Decode(&req); err != nil {
+	if err := json.NewDecoder(c).Decode(&req); err != nil {
 		return
 	}
 	var resp response