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>

tests/test_inventory.py

@@ -1,6 +1,8 @@
 """Tests for the M5 system inventory (render + dict round-trip; collect on real system)."""
 
+import tempfile
 import unittest
+from pathlib import Path
 
 from rigdoctor.core import inventory
 from rigdoctor.core.inventory import Section
@@ -26,5 +28,31 @@ class InventoryTests(unittest.TestCase):
         self.assertIn("- **Model:** Test CPU", md)
 
 
+class PcieLinkTests(unittest.TestCase):
+    def test_gen_mapping(self):
+        self.assertEqual(inventory._gen("16.0 GT/s PCIe"), 4)
+        self.assertEqual(inventory._gen("8.0 GT/s PCIe"), 3)
+        self.assertIsNone(inventory._gen(""))
+
+    def _fake_dev(self, cur_s, cur_w, max_s, max_w) -> Path:
+        d = Path(tempfile.mkdtemp())
+        (d / "current_link_speed").write_text(cur_s)
+        (d / "current_link_width").write_text(cur_w)
+        (d / "max_link_speed").write_text(max_s)
+        (d / "max_link_width").write_text(max_w)
+        return d
+
+    def test_link_at_full_speed(self):
+        dev = self._fake_dev("16.0 GT/s PCIe", "4", "16.0 GT/s PCIe", "4")
+        self.assertEqual(inventory._link_desc(dev), "PCIe Gen4 x4")
+
+    def test_link_downtrained_flags_capability(self):
+        dev = self._fake_dev("8.0 GT/s PCIe", "4", "16.0 GT/s PCIe", "4")
+        self.assertEqual(inventory._link_desc(dev), "PCIe Gen3 x4 (capable of Gen4 x4)")
+
+    def test_non_nvme_has_no_link(self):
+        self.assertEqual(inventory._nvme_link("sda"), "")
+
+
 if __name__ == "__main__":
     unittest.main()