fix: harden restart_claude_desktop across platforms (#33)

- Linux (and any non-desktop platform): refuse instead of 'pkill claude',
  which substring-matched running Claude Code CLI sessions and relaunched
  the CLI, not a desktop app. New restart_supported() gates the button.
- macOS: wait (<=5s) for the old instance to exit before 'open -a Claude'
  so the relaunch can't re-activate the dying process. Runs off the UI
  thread via a RestartWorker.
- Windows: verify the Start-menu shortcut exists BEFORE taskkill, so an
  MSIX/Store install is never killed without a relaunch path.

Closes #33

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

bcc.py

@@ -1423,6 +1423,17 @@ class AboutDialog(QDialog):
         QDesktopServices.openUrl(QUrl(self._release_url or core.RELEASES_URL))
 
 
+# --------------------------------------------------------------------------- #
+# Restart worker: core.restart_claude_desktop() blocks up to ~5 s on macOS
+# waiting for the old instance to exit, so it must run off the UI thread.
+# --------------------------------------------------------------------------- #
+class RestartWorker(QThread):
+    done = Signal(object)  # core.RestartResult
+
+    def run(self):
+        self.done.emit(core.restart_claude_desktop())
+
+
 # --------------------------------------------------------------------------- #
 # Main window
 # --------------------------------------------------------------------------- #
@@ -2284,18 +2295,30 @@ class MainWindow(QMainWindow):
     def _offer_restart_button(self):
         """Show the 'Restart Claude Desktop' button after a successful save,
         but only when the just-saved profile is Claude Desktop -- restarting
-        makes no sense for Claude Code, which has no GUI process to bounce."""
-        if self.current_profile and core.profile_targets_claude_desktop(self.current_profile):
+        makes no sense for Claude Code, which has no GUI process to bounce --
+        and only on platforms where Claude Desktop exists (never Linux, where
+        'claude' is the Claude Code CLI)."""
+        if (
+            self.current_profile
+            and core.profile_targets_claude_desktop(self.current_profile)
+            and core.restart_supported()
+        ):
             self.restart_btn.show()
         else:
             self.restart_btn.hide()
 
     def _restart_claude_desktop(self):
         self.restart_btn.setEnabled(False)
-        try:
-            result = core.restart_claude_desktop()
-        finally:
-            self.restart_btn.setEnabled(True)
+        self.restart_btn.setText("Restarting…")
+        # Held on self (MainWindow outlives the worker); replaced only after
+        # done re-enables the button, so a running thread is never dropped.
+        self._restart_worker = RestartWorker()
+        self._restart_worker.done.connect(self._on_restart_done)
+        self._restart_worker.start()
+
+    def _on_restart_done(self, result):
+        self.restart_btn.setEnabled(True)
+        self.restart_btn.setText("Restart Claude Desktop")
         self.restart_btn.hide()
         if result.success:
             self.status.setText(f"{self.status.text()}  ·  {result.detail}")