feat: add public index page with censored playlist and live reveals

Public-facing page at / shows the current show's playlist with tracks
obscured until the admin marks them as announced. Tracks reveal in
real-time via a new unauthenticated /ws/public WebSocket. Server-side
censorship on /public/playlist strips track details from unannounced
items and sanitizes announced tracks to only expose frontend-needed
fields (no raw_json, track_id, etc). Past episodes are browsable with
fully revealed but sanitized tracklists.

Also fixes RuntimeError on backfill shutdown by closing the httpx
client on the same event loop that created it.

Made-with: Cursor

src/ntr_fetcher/main.py

@@ -49,18 +49,22 @@ def run() -> None:
 
     if args.init:
         sc = SoundCloudClient()
-        asyncio.run(
-            run_backfill(
-                db=db,
-                soundcloud=sc,
-                soundcloud_user=settings.soundcloud_user,
-                show_day=settings.show_day,
-                show_hour=settings.show_hour,
-                anchor_episode=args.show,
-                anchor_aired=args.aired,
-            )
-        )
-        asyncio.run(sc.close())
+
+        async def _backfill_and_close():
+            try:
+                await run_backfill(
+                    db=db,
+                    soundcloud=sc,
+                    soundcloud_user=settings.soundcloud_user,
+                    show_day=settings.show_day,
+                    show_hour=settings.show_hour,
+                    anchor_episode=args.show,
+                    anchor_aired=args.aired,
+                )
+            finally:
+                await sc.close()
+
+        asyncio.run(_backfill_and_close())
         logger.info("Backfill complete")
         return