feat(displays): monitors w/ resolution+refresh in Inventory; flag sub-max refresh in Health — 0.39.0

New core/displays.py reads connected monitors via GNOME Mutter DisplayConfig over
D-Bus (busctl --json; works on X11 + Wayland), falling back to xrandr on other X11
desktops. Inventory's Display section now lists each monitor's resolution + current
refresh (e.g. 'DP-1 · Samsung LC34G55T: 3440x1440 @ 165 Hz'). System Health
(check_displays) flags a monitor running below its max refresh AT THE CURRENT
resolution (e.g. 165 Hz panel set to 60 Hz) — never suggests lowering resolution.
+tests (Mutter JSON + xrandr parsers, health check).

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

tests/test_health.py

@@ -4,11 +4,12 @@ import unittest
 from pathlib import Path
 from unittest import mock
 
-from rigdoctor.core import health
+from rigdoctor.core import displays, health
 from rigdoctor.core.health import (
     CRITICAL,
     INFO,
     WARNING,
+    check_displays,
     check_pcie_links,
     run_health_checks,
     scan_journal_text,
@@ -81,5 +82,20 @@ class PcieLinkCheckTests(unittest.TestCase):
             self.assertEqual(check_pcie_links(), [])
 
 
+class DisplayCheckTests(unittest.TestCase):
+    def test_lower_than_max_refresh_is_flagged(self):
+        mon = displays.Monitor("DP-1", "Samsung LC34G55T", 3440, 1440, 60.0, 165.0)
+        with mock.patch("rigdoctor.core.displays.collect", return_value=[mon]):
+            findings = check_displays()
+        self.assertEqual(len(findings), 1)
+        self.assertEqual(findings[0].severity, INFO)
+        self.assertIn("165", findings[0].title)
+
+    def test_at_max_refresh_no_finding(self):
+        mon = displays.Monitor("DP-1", "Samsung LC34G55T", 3440, 1440, 165.0, 165.0)
+        with mock.patch("rigdoctor.core.displays.collect", return_value=[mon]):
+            self.assertEqual(check_displays(), [])
+
+
 if __name__ == "__main__":
     unittest.main()