feat(feed): accent-insensitive search (unaccent)

Feed text search used plain ILIKE, which is case- but not diacritic-insensitive, so 'tiesto'
missed the many titles spelled 'Tiësto' — a search that ingested ~45 results showed only ~12.
Enable the postgres unaccent extension (migration 0029) and wrap both sides of the title/
channel match in unaccent(), so 'tiesto' now matches 'Tiësto'. Applies to feed, count and
facets alike.

backend/app/routes/feed.py

@@ -205,8 +205,15 @@ def _filtered_query(
         ) + timedelta(days=1)
         query = query.where(Video.published_at < end)
     if q:
-        like = f"%{q}%"
-        query = query.where(or_(Video.title.ilike(like), Channel.title.ilike(like)))
+        # Accent-insensitive: unaccent() both sides so "tiesto" matches "Tiësto" (ILIKE alone
+        # is case- but not diacritic-insensitive). unaccent is enabled by migration 0029.
+        like = func.unaccent(f"%{q}%")
+        query = query.where(
+            or_(
+                func.unaccent(Video.title).ilike(like),
+                func.unaccent(Channel.title).ilike(like),
+            )
+        )
 
     if tags:
         # AND across tag categories (e.g. language AND topic narrows), OR within a