Sync local clipboard to a tab when it becomes visible

Only the visible tab syncs the clipboard, but a tab in the background
missed local clipboard changes and kept a stale remote clipboard when
switched to, so with two RDP/VNC sessions only the one last copied in
worked. A tab now pushes the current local clipboard to its remote on
show.

Bump version to v2026.9.26.2.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/PROGRESS.md

@@ -242,6 +242,11 @@ Delivered:
   and not-yet-ready-channel copies are logged to the session event log
   (with a line per copy sent/received) instead of silently dropped. Not
   reproduced locally; needs confirmation from real use
+- Follow-up to the clipboard fix above: restricting sync to the visible
+  tab left a tab that had been in the background with a stale remote
+  clipboard when switched to (with two RDP sessions only the one last
+  copied in worked). A tab now pushes the current local clipboard to its
+  remote whenever it becomes visible
 - Robustness fix: an unrecognized `FramebufferUpdate` rectangle encoding
   used to abort the connection generically; `kAnnouncedEncodings` is now
   the single source of truth for what `SetEncodings` announces and what