- Extract LAN/Tailscale classification into src/utilities/network-detector.js
(detectInterfaceIps, isTailscaleIP, isPrivateLanIP). The route handler in
src/app.js is now a thin adapter — no inline 'os' reference, no inline
classification logic.
- Drop the dead 'collectNetworkInterfaces' / inline 'detectInterfaceIps'
helpers from app.js (the original ReferenceError shape).
- Add __tests__/network-ips-route.test.js (16 tests):
- Detector unit tests for Tailscale CGNAT (100.64/10) and RFC 1918 LAN
ranges with malformed-input guards.
- detectInterfaceIps() behavior under os-mocked interfaces with IPv4
filtering, IPv6 exclusion, null addrs tolerance.
- Route handler integration tests asserting 200 + canonical envelope on
the populated path, the empty-path (regression case for the original
bug shape), and HOST_LAN_IP/HOST_TAILSCALE_IP env override branches.
- Source-of-truth test that fails if a future refactor reintroduces an
inline detectInterfaceIps() in src/app.js or references 'os' without
a prior require('os') line.
- Fix latent ESLint Error in backup-manager.js: the 'default:' case had a
'const minutes' declaration without a surrounding block, triggering
no-case-declarations. Added the block braces.
Pre-fix baseline: no test exercised this route, so the 1071-test suite
passed despite the 500. Post-fix: 1087/1087 tests pass (+16 new), zero new
ESLint warnings (10 pre-existing warnings in backup-manager.js unrelated
to this commit).
