refactor(logs): name every logger after its module, and hold it there

25 literal names covered 34 modules. plex/client.py, plex/stream.py,
plex/subtitles.py, plex/sync.py and two Plex route modules all called themselves
`siftlode.plex`; downloads/pipeline.py called itself `siftlode.worker`;
routes/channels.py called itself `siftlode.api`. The `logger` column is in every
stored row so E22.6's console can filter on it, and so an operator can pin a level
to one part of the system — neither works when six modules share a name.

`logs.get_logger(__name__)` derives it: app/plex/sync.py -> siftlode.plex.sync.
One name per module, and it cannot drift from the file it sits in.
tests/test_logger_names.py pins the derivation, that everything stays under the
one `siftlode` tree the handler and the tests attach to, and that no module
hand-rolls a name again unless the line says why (`# logger-name-ok: <why>`).
Two do: get_logger's own call, and `siftlode.http`, which is named for the traffic
it carries rather than the module it lives in — it replaced uvicorn's access log
and is what an operator pins when they want request lines and nothing else.

app/scheduler.py called its logger `logger`; every other module calls it `log`.

ruff gains LOG, G, T20, TRY400, TRY401 and S112. Four findings cleared with them:
worker.py logged `str(exc)[:120]` where the traceback was the whole question, and
three prints/f-strings that are deliberate now say so on the line. S110 and BLE001
stay off until S3 — 23 handlers are outstanding and each is a judgement about one
of them; enabling the rules first would just mean 23 blanket noqas.

backend/app/worker.py

@@ -16,7 +16,6 @@ Design:
   * Crash-safe: on startup, orphaned `running` jobs are requeued and `downloading` assets reset.
 """
 
-import logging
 import os
 import shutil
 import signal
@@ -45,8 +44,7 @@ from app.downloads.jobdb import (
 from app.downloads.status import STOPPED_BY_ROUTE, JobStatus
 from app.models import DownloadJob, MediaAsset
 
-log = logging.getLogger("siftlode.worker")
-
+log = logs.get_logger(__name__)
 _stop = threading.Event()
 
 
@@ -73,13 +71,14 @@ def _wait_for_schema(timeout: float = 300.0) -> bool:
             with SessionLocal() as db:
                 db.execute(text("SELECT 1 FROM download_jobs LIMIT 1"))
             return True
-        except Exception as exc:  # noqa: BLE001 — table not migrated yet / DB not up yet
+        except Exception:  # noqa: BLE001 — table not migrated yet / DB not up yet
             if time.monotonic() > deadline:
-                log.error(
-                    "download schema still absent after %ss — the API's migrations have not landed; "
-                    "exiting so the container restarts: %s",
+                # The traceback, not `str(exc)[:120]`: this is the last thing the worker says
+                # before it exits, and which driver call failed is the whole question.
+                log.exception(
+                    "download schema still absent after %ss — the API's migrations have not "
+                    "landed; exiting so the container restarts",
                     timeout,
-                    str(exc)[:120],
                 )
                 return False
             log.info("waiting for the database schema (API migrations)…")