fix: make SQLite searches Unicode case-insensitive

[romasku]

SQLite's built-in lower() only handles ASCII. SQLAlchemy implements ilike() on SQLite using lower(), so lowercase Ukrainian queries (and more generally, non-ASCII Unicode) did not match names beginning with uppercase Ukrainian. In full-text search, this meant черв could miss Червоний.

Here I register a Unicode-aware lower() implementation on every aiosqlite connection, and add a separate integration case that stores Червоний and searches for its lowercase form.

Disclaimer: AI-assisted