v1.8.36: fix fullscreen toggle — _is_detached flag prevents re-embed conflict

- Added _is_detached flag to EmbeddedRDP (set in detach(), cleared in reattach())
- _monitor_tick() skips try_reembed() when window is intentionally detached
- Prevents race condition: monitor tick no longer re-embeds fullscreen window
- Added plans/test-rdp.md — RDP testing documentation
- build.py auto-cleanup removed v1.8.31

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/tabs/launch_tab.py

@@ -384,7 +384,8 @@ class LaunchTab(ctk.CTkFrame):
                 self._on_rdp_exited()
                 return
 
-            if not self._embedded_rdp.is_embedded():
+            # Skip re-embed check when intentionally detached (fullscreen)
+            if not self._embedded_rdp._is_detached and not self._embedded_rdp.is_embedded():
                 # HWND invalid or reparented — mstsc reconnected with new window
                 log.info("RDP window lost, attempting re-embed...")
                 self._rdp_frame.update_idletasks()