Document and parameterize Point2 conservation setup

[ReidSurmeier]

Summary

• preserve the July wiring packet and distinguish the NV3210 display chain from historical MRV412 firmware
• add the repository documentation contract, ADRs, hermetic CI, and opt-in Point2 integration tests
• support explicit Original/Point2 installation profiles and Debian 12/13 Chromium binaries
• remove a plaintext legacy login credential from the public README

Validation

• 12 repository tests passed; 5 live Point2 tests skipped by default
• 5 wiring contract tests passed
• Python compile, shell syntax, default/Point2 service rendering, and sanitized systemd verification passed
• git diff whitespace and working-tree/history secret scans passed
• GitNexus staged impact: low risk, no affected execution flows

Runtime boundary

Point2 is offline, so this PR does not deploy to it and makes no current hardware-state claim. The existing dirty home checkout remains preserved and untouched.