feat(gui): add a "Check for updates" button to the sidebar

Force an immediate version check instead of waiting for the 30-minute poll.
Reuses the background update check; no-op while awaiting restart after an update.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/rigdoctor/__init__.py

@@ -1,3 +1,3 @@
 """RigDoctor — modular hardware monitoring & crash diagnostics for Linux gamers."""
 
-__version__ = "0.1.1"
+__version__ = "0.2.0"

src/rigdoctor/gui/main_window.py

@@ -134,6 +134,11 @@ class MainWindow(QMainWindow):
         changelog_btn.setCursor(Qt.CursorShape.PointingHandCursor)
         changelog_btn.clicked.connect(self._show_changelog)
         v.addWidget(changelog_btn)
+        check_btn = QPushButton("Check for updates")
+        check_btn.setObjectName("LinkButton")
+        check_btn.setCursor(Qt.CursorShape.PointingHandCursor)
+        check_btn.clicked.connect(self._manual_check)
+        v.addWidget(check_btn)
 
         # Update state (filled in by the background check).
         self._update_label = QLabel("checking for updates…")
@@ -189,6 +194,12 @@ class MainWindow(QMainWindow):
             self._update_label.setText("update failed")
             self._update_btn.setEnabled(True)
 
+    def _manual_check(self) -> None:
+        if self._applied:
+            return
+        self._update_label.setText("checking for updates…")
+        self._start_update_check()
+
     def _start_update_check(self) -> None:
         threading.Thread(target=self._check_updates, daemon=True).start()