Fix Radarr discovery: activity log seeding + calibrate threshold

- Stage 1 rewritten to use Emby activity log (playback.stop events)
  with ItemId batch-fetching instead of per-library UserData sort;
  SortBy=DatePlayed requires UserId context and errored server-wide

- Scoring simplified: recency (0-50) + play frequency across all
  users (0-50); CommunityRating is not exposed by Emby Items API
  so TMDB rating scoring moved entirely to Stage 2

- Batch IDs in groups of 100 — 1500+ unique item IDs in a 30-day
  window exceeded GET URL limits on a single request

- Threshold lowered to 50 (from 60); with diverse-genre seeds,
  recommendations rarely appear across multiple seeds so breadth
  score stays at 10/40 — threshold 50 yields ~5 adds per run at
  good quality (rating 7.0+, 1k+ votes)

- HOST1_TMDB_API_KEY moved to sit under Radarr section in
  master_host1.conf where it logically belongs

master_host1.conf

@@ -572,6 +572,7 @@
 # ━━━ Radarr ━━━
     HOST1_RADARR_URL="http://localhost:7878"
     HOST1_RADARR_API_KEY="d43a3ec6cf1549edb4af0cc63f98b2a9"
+    HOST1_TMDB_API_KEY="3dac5e2e49b5540472d2eafec4f01260"
     HOST1_RADARR_MOVIES_ROOT="/mnt/user/Movies"
 
 # Note: stand-up_comedy in both Radarr + Sonarr — movie specials and TV specials, one folder