fix(sync): strip blank lines from channel descriptions before storing

YouTube channel descriptions pad their contact/link blocks with runs of blank
lines, which the About popover renders verbatim (whitespace-pre-wrap) — wasted
space and storage, and noise in the search_vector. Add normalize_description()
and apply it at both channel store sites (full details + initial import) so the
DB holds the clean text. New channels are clean immediately; existing rows heal
on their next metadata re-sync. Unit-tested in test_utils.

backend/app/utils.py

@@ -36,3 +36,15 @@ def to_tsquery_str(q: str) -> str | None:
         return None
     tokens[-1] = tokens[-1] + ":*"
     return " & ".join(tokens)
+
+
+def normalize_description(text: str | None) -> str | None:
+    """Strip whitespace-only lines from a channel/video description before storing. YouTube
+    descriptions pad contact/link blocks with runs of blank lines; keeping them wastes storage,
+    bloats the About popover, and adds nothing to the search document. Drops purely-empty lines and
+    right-strips each kept line. None stays None; all-blank collapses to "". Applied at the
+    sync/store site so the DB (and the derived search_vector) holds the clean text."""
+    if text is None:
+        return None
+    kept = [line.rstrip() for line in text.splitlines() if line.strip()]
+    return "\n".join(kept)