docs: add PiKVM V4 Plus and TESmart KVM to inventory

[jmgilman]

Summary

• Adds PiKVM V4 Plus (specs from the official product page) and the TESmart 8x1 HDMI KVM switch to reference/hardware-inventory.md
• Both devices already appear in the physical connection map (PHY-004, PHY-005)
• TESmart exact SKU unknown (the 8x1 line has 4K30/4K60/USB3 variants), so only physically certain facts are recorded and the variant is marked unspecified

Validation

• moon run docs:build (mkdocs --strict) passes