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/logs.py

@@ -15,7 +15,7 @@ issue attachment will carry, so it is deliberately flat and stable.
 
 Call sites stay ordinary stdlib logging:
 
-    log = logging.getLogger("siftlode.downloads")
+    log = logs.get_logger(__name__)  # app/downloads/pipeline.py -> siftlode.downloads.pipeline
     log.info("job finished", extra=logs.event("download.job.done", job_id=7, bytes=n))
 
 `event()` is optional — a bare `log.info("…")` still comes out well-formed — but the dotted code is
@@ -401,6 +401,20 @@ _THIRD_PARTY_LEVELS = {
 }
 
 
+def get_logger(name: str) -> logging.Logger:
+    """The logger for one module: `logs.get_logger(__name__)` in `app/plex/sync.py` is
+    `siftlode.plex.sync`.
+
+    The names were literals before, and 25 of them covered 34 modules — six different Plex modules
+    all called themselves `siftlode.plex`, so neither a level pinned per logger nor E22.6's console
+    filter could tell a sync line from a stream line. Derived from `__name__` there is exactly one
+    name per module, it cannot drift from the file it sits in, and `test_logger_names.py` fails if a
+    module hand-rolls one again."""
+    stem = name.removeprefix("app.") if name.startswith("app.") else ""
+    # logger-name-ok: this call IS the derivation
+    return logging.getLogger(f"siftlode.{stem}" if stem else "siftlode")
+
+
 def resolve_level(name: str) -> int:
     """Level name → number. Both ways in (the `LOG_LEVEL` env and the `log_level` admin knob) are
     already held to the `LogLevel` choices, so an unknown name here is a programming error."""
@@ -566,7 +580,10 @@ _REQUEST_ID_RE = re.compile(r"^[A-Za-z0-9._-]{8,64}$")
 # A FAILURE on either still logs at WARNING/ERROR — this lowers the floor, it does not hide.
 _QUIET_PREFIXES = ("/healthz", "/assets/", "/static/")
 
-_request_log = logging.getLogger("siftlode.http")
+# Not `siftlode.logs`: this is the replacement for uvicorn's ACCESS log, and `siftlode.http` is
+# what an operator pins a level on when they want request lines and nothing else. The module it
+# happens to live in is not what the name is about.
+_request_log = logging.getLogger("siftlode.http")  # logger-name-ok: named for the traffic
 
 
 async def log_requests(request, call_next):