server-persisted watch history with position + resume

- POST/GET /api/history: JSON file in data/history.json (50 entries
  kept, top 5 shown on home), upsert per (anime, episode)
- watch position saved every ~10s of playback + on pause/unload
- resume: opening an anime seeks to the saved position unless
  >=95% through (then starts fresh); position shown on home items
- drops localStorage; server is the source of truth (verified:
  fresh watch -> new session resumes at saved pos -> home lists it)

.gitignore

@@ -1,3 +1,4 @@
 .venv/
 __pycache__/
 *.pyc
+data/