feat(inventory): show NVMe PCIe link gen/width, flag downtrains — 0.38.0

Each NVMe drive's Inventory entry now shows its negotiated PCIe link (e.g.
'· PCIe Gen4 x4') from sysfs (current/max link speed+width), and flags drives
running below their capability ('Gen3 x4 (capable of Gen4 x4)') — so you can
confirm a Gen4 SSD is in a Gen4 slot. SATA disks show no PCIe link. Renders in
the GUI Inventory, CLI, and the Markdown/JSON export automatically. +tests.

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

CHANGELOG.md

@@ -5,6 +5,14 @@ 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).
 
+## [0.38.0] - 2026-05-22
+### Added
+- **PCIe link in the Inventory.** Each NVMe drive now shows its negotiated PCIe link next to the
+  model — e.g. `Samsung SSD 980 PRO 1TB (931.5G) · PCIe Gen4 x4` — read from sysfs
+  (`current/max_link_speed` + width). If a drive negotiates below its capability (a slower M.2
+  slot, lane-sharing, or a downtrain) it's flagged: `PCIe Gen3 x4 (capable of Gen4 x4)`. So you
+  can confirm a Gen4 SSD is actually in a Gen4 slot. (SATA disks show no PCIe link.)
+
 ## [0.37.1] - 2026-05-22
 ### Fixed
 - **`rigdoctor update` now uses the right method for how RigDoctor was installed.** It detects