Real database vmk_data does not have 'floors_count' column.
This was causing asyncpg.PostgresError on every SELECT that included
floors_count in _SELECT_COLUMNS built from USER_COLUMNS.

Removed from:
- db.py USER_COLUMNS (no longer included in SELECT)
- tools.py describe_schema JSON schema docs

ListingResult.floors_count kept as int|None=None for backward compatibility
with future schema additions — Pydantic safely defaults to None when column
is absent from query result.

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