docs(hardware): identify XTRM-U mainboard (N5 Air) + flag 1Gbps network anomaly

- Mainboard was 'details TBD': Minisforum N5 Air (Meigao F8NAB/N5A), Ryzen 7 255
  + 780M, 64GB DDR5-5600, USB4/TB, free OCuLink + PCIe x8 + M.2; OS -> Unraid 7.3.1
- Network: 10G/5G NICs but link only 1Gbps (eth1 degraded at 10Mb/s) — flagged

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/04-HARDWARE-INVENTORY.md

@@ -107,14 +107,25 @@
 | **Role** | Production Server |
 | **Location** | 10" Rack U1-U4 |
 | **IP** | 192.168.10.20 |
-| **OS** | Unraid 6.x |
+| **OS** | Unraid 7.3.1 (kernel 6.18.33) |
 
-**Motherboard:** Replaced 2026-02-24 (new board, details TBD)
+**Mainboard (replaced 2026-02-24):** Minisforum **N5 Air** — Meigao `F8NAB` / system `N5A` (AMI BIOS 1.01, 2025-10-24). Verified 2026-06-30.
 
-**Network:**
-| Interface | MAC | Speed |
-|-----------|-----|-------|
-| br0 | 38:05:25:35:8E:7A | 2.5G |
+**CPU/APU:** AMD Ryzen 7 255 (Phoenix/Hawk Point, 8C/16T) + Radeon **780M** iGPU (gfx1103)
+**RAM:** 64 GB DDR5-5600 (2× 32 GB SODIMM); ~46 GiB usable by OS (rest reserved, likely iGPU UMA), 0 swap
+**Connectivity:** USB4 / Thunderbolt (AMD Pink Sardine)
+
+**Expansion (for eGPU / AI):**
+| Slot | Status | Notes |
+|------|--------|-------|
+| OCuLink (PCIe 4.0 x4) | built-in | data only — eGPU powered by PSU in the dock, not the N5 Air |
+| PCIe x8 (J96) | free | usable, but no internal case space for a GPU |
+| M.2 Socket (J132) | free | spare (M.2→OCuLink also possible) |
+| 3× M.2 (J98/J109/J100) | in use | NVMe cache pool |
+
+**Network:** onboard Realtek **RTL8127 (10GbE-capable)** + **RTL8126 (5GbE-capable)**, bonded → `bond0` → `br0` (MAC `38:05:25:35:8E:7B`).
+
+⚠️ **Actual link only 1 Gbps** (verified 2026-06-30): `eth0` = 1000 Mb/s active, `eth1` = **10 Mb/s** (degraded bond member). 10G/5G hardware not running at speed — likely switch port (ZX1 is 2.5G) / cabling / bond fault. Worth investigating.
 
 **Storage:**
 | Device | Model | Size | Role | Status |