multi-stage Dockerfile + player recap styles

Dockerfile: split into whisperx-base and runtime stages so app-only
changes skip the 10min pip install on rebuild. Example compose updated.

Player recap: replace hardcoded 'story so far' prompt with selectable
styles (story/diary/bullets/custom) via dropdown in Setup and Settings.

Settings: add NAT20_ONBOARDING_COMPLETED env var; fix merge logic so
env vars properly override defaults (not just empty DB values).

backend/app/routers/notes.py

@@ -26,7 +26,11 @@ def generate_notes(session_id: str):
 
     def run(progress_cb):
         turns = load_turns(Path(session["transcript_path"]), speaker_map)
-        dm_notes, player_recap = summarize_session(turns, settings, progress_cb=progress_cb)
+        dm_notes, player_recap = summarize_session(
+            turns, settings, progress_cb=progress_cb,
+            player_recap_style=settings.get("player_recap_style"),
+            player_recap_custom_prompt=settings.get("player_recap_custom_prompt"),
+        )
         with db.tx() as conn:
             conn.execute(
                 "INSERT INTO notes (session_id, dm_notes, player_recap, generated_at) VALUES (?, ?, ?, ?) "