fix(logs): rule on every swallowed exception in the backend

114 exception handlers neither logged nor re-raised. The defect was never that
they are silent — plenty of them should be — it is that their silence said
nothing, so nobody could tell a decision from an oversight. Each one has now been
read. 44 got a line; the other 70 carry `# silent-ok: <why>`.

What the silent ones had been hiding, in the cases that got a line:
- A failed ffprobe sent every HDR file down the 8-bit pipeline, so playback
  degraded to a software transcode with nothing saying why; a failed audio probe
  collapsed a multi-audio file to one track and the player showed no language
  picker; a failed first-PTS probe left subtitles seconds out of sync.
- A subtitle sidecar that existed but would not parse made a PARTIAL track read as
  complete, permanently — the viewer loses every cue past the cached window.
- An unreadable crop/trim/cut-list in an edit spec was dropped, so the clip came
  out uncropped, untrimmed, or shorter than the one the user built.
- A dropped `max_height` downloaded at best quality against an explicit cap.
- A failed videos.list enrich made every candidate undroppable-from-judgement and
  therefore dropped: a working search rendered as "no results".
- An unusable password hash answered as "wrong password", locking the owner out
  and telling them they mistyped; a rotated TOKEN_ENCRYPTION_KEY turned every
  stored token into "not connected".
- A stored admin setting that would not coerce fell back to the env default while
  the settings page went on showing the saved value.
- A one-off InnerTube config failure pinned the whole process to the hard-coded
  fallback key, and searches return nothing when that goes stale.
- The HLS sweep reported 0 swept — like a clean run — when it could not list its
  own root, leaving every crashed session's segments on disk forever.

Four of them are counted rather than logged per item (dropped cues, dropped cut
list segments, unreclaimed GC files) and reported once per call, because the
alternative is one line per cue over a whole subtitle track.

ruff gains S110 and BLE001. Every blind `except Exception` that remains carries
`# noqa: BLE001 — <why>`, which is the point: catching everything is sometimes
right, and always worth a sentence. plex/sync.py's three best-effort backfill
catches now keep the traceback — a blind catch over a batch that fetches AND
writes could be Plex, the database or our own bug, and `%s` of the exception told
them apart badly. main.py's boot-time log-level read likewise.

logs.event's `code` is positional-only now: `event("x", code=...)` was a TypeError,
and `code` is exactly the word a caller reaches for when the thing that failed has
one of its own.

tests/test_swallowed_exceptions.py is the wider rule ruff cannot see: a handler
that neither logs nor re-raises must say why. Both cases mutation-checked — a
marker removed and a log line removed each fail it, naming the handler.

backend/app/routes/search.py

@@ -130,6 +130,13 @@ def _ingest_candidates(
             apply_channel_details(db, details)
             db.commit()
         except YouTubeError:
+            # The stubs remain and the details can be backfilled later — but until they are, those
+            # channels sit in the results with no thumbnail and no subscriber count, looking like
+            # channels that have neither.
+            log.warning(
+                "the channels found by a search could not be enriched",
+                extra=logs.event("search.channel_enrich_failed", channels=len(new_channel_ids)),
+            )
             db.rollback()  # details can be backfilled later; the stubs remain
 
     # 2) Video stubs, flagged via_search. Existing rows keep their flags (ON CONFLICT DO
@@ -159,6 +166,12 @@ def _ingest_candidates(
         with quota.attribute(user.id, quota.QuotaAction.VIDEOS_ENRICH):
             detail_by_id = {it["id"]: it for it in yt.get_videos(ids)}
     except YouTubeError:
+        # Every candidate then stays unenriched, and an unenriched video cannot be judged live or
+        # Short — so it is dropped. A working search returns nothing and reads as "no results".
+        log.warning(
+            "the videos found by a search could not be enriched",
+            extra=logs.event("search.video_enrich_failed", candidates=len(ids)),
+        )
         detail_by_id = {}
     enriched_at = datetime.now(
         timezone.utc