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>

CHANGELOG.md

@@ -5,6 +5,15 @@ All notable changes to RigDoctor are recorded here. Format follows
 (`MAJOR.MINOR.PATCH`, pre-1.0). `__version__` and `pyproject.toml` must match the git
 release tag (so the auto-updater, D18, can compare versions).
 
+## [0.40.0] - 2026-05-22
+### Added
+- **RAM speed / XMP-EXPO check.** Inventory now shows each module's configured speed and, when it's
+  below the rated speed, the rating (e.g. `4800 MT/s (rated 5600)`); **System Health** flags it
+  ("RAM at 4800 MT/s (rated 5600 MT/s)") with the fix — enable XMP/EXPO in BIOS. With the profile
+  off, dmidecode only reports the JEDEC base, so the rated speed is read from both dmidecode and
+  the part number (matched against known DDR5 speed grades, so no false positives). Needs dmidecode
+  (root / launch elevation). Completes the "underperforming hardware" trio with PCIe gen + refresh.
+
 ## [0.39.0] - 2026-05-22
 ### Added
 - **Displays in the Inventory.** A new `core/displays.py` lists each connected monitor with its