refactor: address /code-review — rename uploader_url() to build_uploader_url()

The R12 S3 underscore-publish left worker.uploader_url() sharing a name with the
`uploader_url` model attribute and the yt-dlp `"uploader_url"` info-dict key. The
function is now build_uploader_url() — the attribute, dict key, log line and
docstrings keep the plain `uploader_url` name. Rename touches only the def, its
two call sites, and the backfill import; no behaviour change (ruff clean,
pytest 193).

backend/app/downloads/backfill.py

@@ -21,7 +21,7 @@ from app.db import SessionLocal
 from app.downloads import edit as editmod
 from app.downloads import formats, service
 from app.models import MediaAsset
-from app.worker import uploader_url
+from app.worker import build_uploader_url
 
 log = logging.getLogger("siftlode.backfill")
 
@@ -73,7 +73,7 @@ def run() -> dict:
             if a.uploader_url is None and _should_refetch(a):
                 url = a.source_webpage_url or service.source_url(a.source_kind, a.source_ref)
                 info = _extract_meta(url)
-                uu = uploader_url(info) if info else None
+                uu = build_uploader_url(info) if info else None
                 if uu:
                     a.uploader_url = uu
                     filled_url += 1

backend/app/worker.py

@@ -262,7 +262,7 @@ def _finish_from_cache(job_id: int, asset_id: int) -> None:
         db.commit()
 
 
-def uploader_url(info: dict) -> str | None:
+def build_uploader_url(info: dict) -> str | None:
     """The channel/uploader page URL for the auto-clickable channel line. YouTube gives a
     `channel_url`/`uploader_url` directly; Facebook gives neither but exposes a numeric
     `uploader_id` (the page id) that resolves at facebook.com/<id>. Returns None for sources with
@@ -290,7 +290,7 @@ def _fill_asset_meta_early(asset_id: int, info: dict) -> None:
         # the final title with its own source_ref fallback.
         asset.title = normalize_title(info.get("title")) or info.get("id")
         asset.uploader = info.get("uploader") or info.get("channel")
-        asset.uploader_url = uploader_url(info)
+        asset.uploader_url = build_uploader_url(info)
         asset.thumbnail_url = info.get("thumbnail")
         asset.duration_s = int(info["duration"]) if info.get("duration") else None
         asset.upload_date = _parse_upload_date(info.get("upload_date"))
@@ -638,7 +638,7 @@ def _download(job_id: int, asset_id: int, source_kind: str, source_ref: str, spe
                 asset.acodec = info.get("acodec") if info.get("acodec") not in (None, "none") else None
                 asset.title = meta.title
                 asset.uploader = meta.uploader
-                asset.uploader_url = uploader_url(info)
+                asset.uploader_url = build_uploader_url(info)
                 asset.upload_date = meta.upload_date
                 asset.thumbnail_url = meta.thumbnail_url
                 # Record a self-hosted poster for every download: it's the reliable link-preview