feat: add PostgreSQL full-text search ...

- Add generated search_vector tsvector column with immutable wrapper
  to_tsvector_simple() for mixed ru/ua text
- Add GIN index ix_property_listings_search_vector_gin
- Add PropertyRepository.search_fulltext() using plainto_tsquery(simple)
  and ts_rank_cd() with optional filters
- Add POST /api/v1/search/fulltext endpoint (120/min rate limit)
- Add FulltextSearchRequest/Result/Response schemas
- Update alembic.ini to use Docker PostgreSQL on port 5433

Co-Authored-By: Claude <noreply@anthropic.com>