feat(memory): flag RAM below rated speed (XMP/EXPO not enabled) — 0.40.0

Inventory shows configured RAM speed + the rated speed when lower
('4800 MT/s (rated 5600)'); System Health flags it with the fix (enable
XMP/EXPO in BIOS). With the profile off dmidecode only reports the JEDEC base,
so the rated speed comes from dmidecode's max OR the part number, matched against
known DDR5 speed grades to avoid false positives. inventory.module_speed() shared
by both; needs dmidecode (root/launch elevation). +tests (incl. the user's
CMK..5600 kit → (4800, 5600)). Completes the underperforming-hardware trio with
PCIe gen + refresh rate.

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

tests/test_health.py

@@ -10,6 +10,7 @@ from rigdoctor.core.health import (
     INFO,
     WARNING,
     check_displays,
+    check_memory_speed,
     check_pcie_links,
     run_health_checks,
     scan_journal_text,
@@ -97,5 +98,26 @@ class DisplayCheckTests(unittest.TestCase):
             self.assertEqual(check_displays(), [])
 
 
+class MemorySpeedCheckTests(unittest.TestCase):
+    def _dmi(self, configured, part):
+        return {"memory": [{"Configured Memory Speed": configured, "Speed": configured,
+                            "Part Number": part}]}
+
+    def test_flags_unapplied_expo(self):
+        dmi = self._dmi("4800 MT/s", "CMK32GX5M2B5600Z36")
+        with mock.patch("rigdoctor.core.elevation.privileged", return_value=None), \
+             mock.patch("rigdoctor.core.inventory._dmidecode", return_value=dmi):
+            findings = check_memory_speed()
+        self.assertEqual(len(findings), 1)
+        self.assertEqual(findings[0].severity, INFO)
+        self.assertIn("5600", findings[0].title)
+
+    def test_no_flag_at_rated(self):
+        dmi = self._dmi("5600 MT/s", "CMK32GX5M2B5600Z36")
+        with mock.patch("rigdoctor.core.elevation.privileged", return_value=None), \
+             mock.patch("rigdoctor.core.inventory._dmidecode", return_value=dmi):
+            self.assertEqual(check_memory_speed(), [])
+
+
 if __name__ == "__main__":
     unittest.main()