Postgres search ignores case but not accents: manutencao misses "Manutenção", agua misses "água". When unaccent extension callable, db.ILIKE and db.SearchRelevanceOrder now wrap both sides in unaccent(). Detected at startup by calling unaccent('a'), so extension outside search_path counts as missing. Without extension, or on MySQL/SQLite: no change. Vikunja never runs CREATE EXTENSION itself.

CI: postgres job enables unaccent, paradedb job stays without, so both paths covered. Postgres paths not verified locally, only via CI.

Saved-filter ILIKE fix from issue already on main (3744b6a). Follow-up, out of scope: filter like operator still case-sensitive on Postgres.

Resolves #4131

How to verify

1. Run Vikunja on Postgres and run CREATE EXTENSION unaccent; in its database, then restart Vikunja. The startup log shows "unaccent extension detected, search is accent-insensitive".
2. Create a project titled "Manutenção" and a task titled "Água".
3. Search for manutencao and agua in the quick-add/search bar.
4. Expected: both the project and the task are found.
   Before this PR: neither is found.
5. Drop the extension (DROP EXTENSION unaccent;) and restart. The same searches find nothing, and search otherwise behaves as before.