chore(feed): Phase 2 #2 backend cleanup — dead return, dup helpers, shared const

- feed.py _filtered_query: drop the dead 2nd return element (status_expr was
  used only internally for WHERE filters; all 3 callers discarded it as _status).
  Now returns (query, rank_expr); fixed the stale docstring.
- youtube/client.py: extract _iter_playlist_items() — iter_my_playlist_video_ids
  and iter_playlist_items_with_ids were near-identical playlistItems paging loops
  (jscpd [173-187]≈[267-281]); both now map over the shared generator.
- sync/videos.py: extract _apply_video_batch() with an on_missing callback —
  enrich_pending and refresh_live shared the fetch-map-apply skeleton, differing
  only in the query and how they retire rows YouTube omits.
- models.py: add LIVE_OR_UPCOMING = ("live","upcoming"); replace the 4 duplicated
  copies (feed.HIDDEN_LIVE, search._LIVE_HIDDEN, videos.py + channels.py inline).

Behavior-neutral. ruff clean on touched files, localdev boots, feed/worker healthy.

backend/app/sync/videos.py

@@ -2,6 +2,7 @@
 uploads playlist, and enrichment via videos.list (duration, stats, category, Shorts
 and livestream classification)."""
 import re
+from collections.abc import Callable
 from concurrent.futures import ThreadPoolExecutor
 from datetime import datetime, timedelta, timezone
 
@@ -10,7 +11,7 @@ from sqlalchemy.dialects.postgresql import insert as pg_insert
 from sqlalchemy.orm import Session
 
 from app import progress, sysconfig
-from app.models import Channel, Video
+from app.models import LIVE_OR_UPCOMING, Channel, Video
 from app.titles import normalize_title
 from app.youtube.client import YouTubeClient, best_thumbnail
 from app.youtube.rss import fetch_channel_feed
@@ -260,6 +261,37 @@ def apply_video_details(video: Video, item: dict) -> None:
     # is_short is decided separately by the youtube.com/shorts probe (run_shorts_classification).
 
 
+def _apply_video_batch(
+    db: Session,
+    yt: YouTubeClient,
+    videos: list[Video],
+    on_missing: Callable[[Video], None],
+) -> int:
+    """Fetch videos.list details for the given rows, apply them (stamping enriched_at), and
+    return how many were applied. Rows YouTube omits (deleted/private) are handled by the
+    caller-supplied `on_missing` so each caller decides how to retire them."""
+    if not videos:
+        return 0
+    items = {it["id"]: it for it in yt.get_videos([v.id for v in videos])}
+    now = _now()
+    applied = 0
+    for video in videos:
+        item = items.get(video.id)
+        if item is None:
+            on_missing(video)
+            continue
+        apply_video_details(video, item)
+        video.enriched_at = now
+        applied += 1
+    db.commit()
+    return applied
+
+
+def _mark_enriched(video: Video) -> None:
+    # Unavailable (deleted/private): stamp so we don't keep retrying.
+    video.enriched_at = _now()
+
+
 def enrich_pending(db: Session, yt: YouTubeClient, limit: int | None = None) -> int:
     limit = limit or sysconfig.get_int(db, "enrich_batch_size")
     videos = (
@@ -267,22 +299,7 @@ def enrich_pending(db: Session, yt: YouTubeClient, limit: int | None = None) ->
         .scalars()
         .all()
     )
-    if not videos:
-        return 0
-    items = {it["id"]: it for it in yt.get_videos([v.id for v in videos])}
-    now = _now()
-    enriched = 0
-    for video in videos:
-        item = items.get(video.id)
-        if item is None:
-            # Unavailable (deleted/private): stamp so we don't keep retrying.
-            video.enriched_at = now
-            continue
-        apply_video_details(video, item)
-        video.enriched_at = now
-        enriched += 1
-    db.commit()
-    return enriched
+    return _apply_video_batch(db, yt, list(videos), _mark_enriched)
 
 
 def refresh_live(db: Session, yt: YouTubeClient, limit: int | None = None) -> int:
@@ -300,7 +317,7 @@ def refresh_live(db: Session, yt: YouTubeClient, limit: int | None = None) -> in
             select(Video)
             .where(
                 or_(
-                    Video.live_status.in_(("live", "upcoming")),
+                    Video.live_status.in_(LIVE_OR_UPCOMING),
                     and_(
                         Video.live_status == "was_live",
                         Video.duration_seconds.is_(None),
@@ -312,23 +329,13 @@ def refresh_live(db: Session, yt: YouTubeClient, limit: int | None = None) -> in
         .scalars()
         .all()
     )
-    if not videos:
-        return 0
-    items = {it["id"]: it for it in yt.get_videos([v.id for v in videos])}
-    now = _now()
-    updated = 0
-    for video in videos:
-        item = items.get(video.id)
-        if item is None:
-            # The broadcast vanished (deleted/private). Stop treating it as live so it
-            # doesn't get refreshed forever; it just becomes an ordinary (dead) row.
-            video.live_status = "none"
-            continue
-        apply_video_details(video, item)
-        video.enriched_at = now
-        updated += 1
-    db.commit()
-    return updated
+
+    def _retire(video: Video) -> None:
+        # The broadcast vanished (deleted/private). Stop treating it as live so it
+        # doesn't get refreshed forever; it just becomes an ordinary (dead) row.
+        video.live_status = "none"
+
+    return _apply_video_batch(db, yt, list(videos), _retire)
 
 
 def run_shorts_classification(db: Session, limit: int | None = None) -> dict: