fix(gui): correct relative import that broke app startup — 0.18.2

The recording indicator (0.18.0) used `from .core import diagnostic`, which
resolves to the non-existent rigdoctor.gui.core and crashed MainWindow on launch.
Fixed to `from ..core import diagnostic`.

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__ = "0.18.1"
+__version__ = "0.18.2"

src/rigdoctor/gui/main_window.py

@@ -263,7 +263,7 @@ class MainWindow(QMainWindow):
         self.inventory_page._run()
 
     def _update_recording(self) -> None:
-        from .core import diagnostic
+        from ..core import diagnostic
 
         status = diagnostic.active()
         if not status: