fix(lint): E402 is on — the ignore meant for main.py had let 11 late imports in elsewhere

ruff.toml ignored E402 everywhere for main.py's logging setup. Measured: 28 hits, of which 11
had nothing to do with it — runner.py's logger line between its imports, models.py importing
canonical_email mid-file, a test constant above its imports, and main.py's own third-party and
mimetypes imports. Those are moved up. What stays after configure_logging in main.py is marked
per statement (noqa E402, logging is configured first), its comment now says why the order
matters (a line logged while importing, not the logger's creation). The register row goes, the
ruff key whitelist loses ignore, and a late import is red again. The T20 comment counts the
third deliberate print (scripts/e2e_seed.py).

backend/app/sync/runner.py

@@ -15,8 +15,6 @@ from sqlalchemy import func, or_, select, update
 from sqlalchemy.orm import Session
 
 from app import logs, progress, quota, sysconfig
-
-log = logs.get_logger(__name__)
 from app.db import SessionLocal
 from app.models import Channel, OAuthToken, Subscription, User
 from app.sync.explore import followed_channel
@@ -35,6 +33,8 @@ from app.sync.videos import (
 from app.youtube.client import YouTubeClient, YouTubeError, is_quota_refusal
 from app.youtube.rss import RssError, fetch_channel_feed
 
+log = logs.get_logger(__name__)
+
 # RSS feeds are free and network-bound, so fetch many at once; DB writes stay single-threaded.
 RSS_POLL_WORKERS = 16
 # Failed channels named in a poll's summary warning; the rest are counted by reason.