CI: lint against reseller-only sources on new cameras

[ch-bas]

Prevent the reseller-source backlog (246 files, see the round-2 audit issue) from growing.

Add a check in scripts/build.js (the existing CI gate, alongside the #124 autotracking lint): fail the build if a camera's sources contains only known reseller/mirror domains (axilogi, tinnes24, securitywholesalers, conrad, manualslib, solarics, zajadacz, seadan) with no official manufacturer domain.

• Warn-or-error: probably error for brand-new entries, so contributors add an official source; but grandfather the existing 246 (only enforce on added/changed files, or maintain a small allowlist for the accepted EOL-catalog cases).
• Document the rule in CONTRIBUTING.md ("official datasheet preferred; reseller-only sources are rejected except documented EOL cases").

[ch-bas]

Closed by #208