v0.12.1 — One version number, your contact not ours

Fixed

• One version number, everywhere. adsb.im's maintainer noticed our
  requests arriving as adsb-3d/1.0, adsb-3d/0.11 and adsb-3d/0.12 on
  the same day (#16). The
  1.0 had been a placeholder in the nginx config since the first commit
  and in both Python services' metadata; the real version lived only in
  package.json. A repo-root VERSION file is now the single source of
  truth: every image copies it at build time, and the settings panel, the
  /api and /acars-api root endpoints, the nginx User-Agent (adsb.im,
  tile providers, tile pre-cache) and track-service's
  adsb-3d/<version> track-service agent all report it. Non-release builds
  carry build metadata (0.12.1+a1b2c3d, +local). scripts/release.sh
  cuts releases and CI refuses to publish when VERSION, package.json
  and the tag disagree.
• Your contact, not ours. The nginx route and tile proxies had the
  project author's email hardcoded in the User-Agent, so every install
  identified itself to adsb.im as the author. The viewer now reads
  ROUTE_API_CONTACT (same variable track-service already used) and sends
  no contact when it is unset, with a warning at start. Please set it.

Changed

• track-service and acars-service images build from the repository root
  (context: . + dockerfile: <service>/Dockerfile) so they can share
  VERSION. Only matters if you build from source; published images are
  unchanged in use.
• The settings panel header shows the running version.