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/tests/test_utils.py

@@ -1,7 +1,7 @@
 """iso(): the single date/datetime→JSON serializer the routes share (R6 S1a)."""
 from datetime import date, datetime, timezone
 
-from app.utils import iso
+from app.utils import iso, normalize_description
 
 
 def test_none_maps_to_none():
@@ -28,3 +28,25 @@ def test_matches_datetime_isoformat_contract():
     # hand-roll `x.isoformat() if x else None`.
     dt = datetime(2020, 1, 2, 3, 4, 5, 678901, tzinfo=timezone.utc)
     assert iso(dt) == dt.isoformat()
+
+
+def test_normalize_description_none_stays_none():
+    assert normalize_description(None) is None
+
+
+def test_normalize_description_drops_blank_lines():
+    # A YouTube contact block padded with runs of blank lines — the waste we strip before storing.
+    raw = "Contact us\n\n\nEmail: a@b.com\n \nInstagram: @x\n\n\n"
+    assert normalize_description(raw) == "Contact us\nEmail: a@b.com\nInstagram: @x"
+
+
+def test_normalize_description_right_strips_and_trims():
+    assert normalize_description("  hi there  \n\n  bye  ") == "  hi there\n  bye"
+
+
+def test_normalize_description_all_blank_collapses_to_empty():
+    assert normalize_description("\n \n\t\n") == ""
+
+
+def test_normalize_description_single_line_unchanged():
+    assert normalize_description("just one line") == "just one line"