docs: make network documentation authoritative

[jmgilman]

Summary

• remove all Lab v1 and historical-source references
• remove provisional hardware mappings, address plans, and open questions
• narrow the design to approved topology, device boundaries, configuration requirements, and verification criteria
• replace evidence-status prose with direct hardware assignments

Verification

• built the documentation with MkDocs strict mode
• confirmed no historical references or uncertainty-language triggers remain
• browser-checked the landing page, ADR, design, and hardware reference