v2.1.3 - optional TMDB Coming Soon fallback

What's changed

• Optional TMDB enrichment for Coming Soon (closes #91, PR #93). When
  Radarr's calendar entry lacks a usable digital/physical release date,
  the server can now fall back to The Movie Database to find one. Movies
  are matched by Radarr tmdbId first and fall back to imdbId via
  TMDB's /find endpoint — title-only matching is deliberately avoided.
• New add-on options / env vars to configure TMDB:
  • tmdb_api_key (env TMDB_API_KEY) — accepts both v3 keys and v4
    read-tokens. Disabled by default (leave blank for identical
    behaviour to 2.1.2).
  • tmdb_region (env TMDB_REGION, default AU) — country/region
    used when reading TMDB release_dates.
  • tmdb_ttl_ms (env TMDB_TTL_MS, default 6 h) — cache TTL for TMDB
    responses.
• Radarr remains the primary source. TMDB is only consulted when
  Radarr lacks usable home-release metadata. Any TMDB digital/physical
  date inside the look-ahead window upgrades the entry to a home
  release; if only a TMDB theatrical date is available it is used as a
  clearly labelled cinema fallback.
• Coming Soon footer prefers home-release dates over theatrical
  (closes #90, PR #92). The earliest qualifying digitalRelease /
  physicalRelease inside the look-ahead window is shown for Radarr
  movies; the kiosk only falls back to inCinemas when no home date
  qualifies, and cinema-only items are tagged with releaseType: 'cinema'
  and prefixed with In cinemas: <date> so the footer is not mistaken
  for home availability. Both the Node server and the frontend-only path
  apply the same rule.
• hasFile === false, monitored filtering, and the configurable
  Coming Soon look-ahead window (coming_soon_lookahead_days, default
  90) are unchanged.
• TMDB failures degrade gracefully: auth, rate-limit, and network
  errors are logged and silently swallowed so Coming Soon never breaks
  because TMDB is unreachable.

Tests

• cd server && node --test test/ — 170 passed, 0 failed, including
  new coverage for the TMDB fallback path (tmdbId/imdbId resolution,
  region-aware release_dates parsing, look-ahead clamping, caching, and
  graceful degradation on auth/network errors) plus existing coverage
  for digitalRelease/physicalRelease selection, earliest-of-eligible
  logic, the hasFile filter, and monitored filtering.
• python3 config.yaml lint (options/schema balance, required keys,
  arch list) — OK.

Packages

• Add-on package version is 2.1.3.
• The addon-v2.1.3 tag has been pushed to trigger the multi-arch GHCR
  build that publishes:
  • ghcr.io/rusty4444/plex-now-showing-amd64:2.1.3 (and :latest)
  • ghcr.io/rusty4444/plex-now-showing-aarch64:2.1.3 (and :latest)
  • ghcr.io/rusty4444/plex-now-showing-armv7:2.1.3 (and :latest)
  • ghcr.io/rusty4444/plex-now-showing-armhf:2.1.3 (and :latest)
  • ghcr.io/rusty4444/plex-now-showing-i386:2.1.3 (and :latest)
• Supervisor pulls the matching 2.1.3 Docker tag for each arch from
  addons/plex-now-showing/config.yaml's version field.