refactor(backend): select() and an inline now everywhere, held by a test

CLAUDE.md's canonical table names SQLAlchemy 2.0 select() and an inline
datetime.now(timezone.utc), and both had drifted: five db.query(...) calls
remained in routes/auth.py and routes/me.py (seven before the demo went),
and four private now helpers stood in sync/videos.py, utils.py (imported
as _now by explore and maintenance), scheduler.py (_now_iso) and the e2e
seed. All are the canonical form now.

Ruff cannot ban a method call on an instance or a function by name, so
tests/test_canonical_patterns.py reads every app module's AST and fails on
a .query(...) call or a now/_now/now_utc helper — seen red on a planted file.

backend/app/sync/videos.py

@@ -22,10 +22,6 @@ log = logs.get_logger(__name__)
 _DURATION_RE = re.compile(r"P(?:(\d+)D)?T(?:(\d+)H)?(?:(\d+)M)?(?:(\d+)S)?", re.IGNORECASE)
 
 
-def _now() -> datetime:
-    return datetime.now(timezone.utc)
-
-
 def parse_iso8601_duration(value: str | None) -> int | None:
     if not value:
         return None
@@ -80,7 +76,7 @@ def apply_rss_feed(db: Session, channel: Channel, entries: list[dict]) -> int:
     time. DB-only — must run on the session's own thread; the network fetch
     (fetch_channel_feed) is kept separate so callers like run_rss_poll can parallelise it."""
     inserted = insert_stubs(db, entries)
-    channel.last_rss_at = _now()
+    channel.last_rss_at = datetime.now(timezone.utc)
     db.add(channel)
     db.commit()
     return inserted
@@ -96,7 +92,9 @@ def stub_from_playlist_item(item: dict, channel_id: str) -> dict | None:
     # published_at is NOT NULL (migration 0068); fall back to now() for the rare item that carries no
     # date at all, so the bulk stub insert never writes a NULL. The enrich pass replaces it if the
     # video's own snippet later yields a real publish date.
-    published = parse_dt(content.get("videoPublishedAt") or snippet.get("publishedAt")) or _now()
+    published = parse_dt(
+        content.get("videoPublishedAt") or snippet.get("publishedAt")
+    ) or datetime.now(timezone.utc)
     return {
         "id": video_id,
         "channel_id": channel_id,
@@ -124,12 +122,14 @@ def backfill_channel_recent(db: Session, yt: YouTubeClient, channel: Channel) ->
     """First pass: newest videos up to the configured count or age cutoff. Records a
     resume cursor for the later deep backfill."""
     if not channel.uploads_playlist_id:
-        channel.recent_synced_at = _now()
+        channel.recent_synced_at = datetime.now(timezone.utc)
         db.add(channel)
         db.commit()
         return 0
 
-    cutoff = _now() - timedelta(days=sysconfig.get_int(db, "backfill_recent_max_days"))
+    cutoff = datetime.now(timezone.utc) - timedelta(
+        days=sysconfig.get_int(db, "backfill_recent_max_days")
+    )
     collected: list[dict] = []
     page_token: str | None = None
     next_cursor: str | None = None
@@ -164,7 +164,7 @@ def backfill_channel_recent(db: Session, yt: YouTubeClient, channel: Channel) ->
             break
         next_cursor = page_token  # whole page consumed, more pages remain
 
-    channel.recent_synced_at = _now()
+    channel.recent_synced_at = datetime.now(timezone.utc)
     channel.backfill_cursor = next_cursor
     channel.backfill_done = done
     inserted = insert_stubs(db, collected)
@@ -264,7 +264,7 @@ def apply_video_details(video: Video, item: dict) -> None:
     if snippet_published:
         video.published_at = snippet_published
     elif not video.published_at:
-        video.published_at = _now()
+        video.published_at = datetime.now(timezone.utc)
     video.thumbnail_url = best_thumbnail(snippet.get("thumbnails")) or video.thumbnail_url
     video.duration_seconds = parse_iso8601_duration(content.get("duration"))
     video.view_count = int(stats["viewCount"]) if stats.get("viewCount") else None
@@ -296,7 +296,7 @@ def _apply_video_batch(
     if not videos:
         return 0
     items = {it["id"]: it for it in yt.get_videos([v.id for v in videos])}
-    now = _now()
+    now = datetime.now(timezone.utc)
     applied = 0
     for video in videos:
         item = items.get(video.id)
@@ -312,7 +312,7 @@ def _apply_video_batch(
 
 def _mark_enriched(video: Video) -> None:
     # Unavailable (deleted/private): stamp so we don't keep retrying.
-    video.enriched_at = _now()
+    video.enriched_at = datetime.now(timezone.utc)
 
 
 def enrich_pending(db: Session, yt: YouTubeClient, limit: int | None = None) -> int: