Fix user search on newer Nextcloud

Fixed

• User search/count broken on newer Nextcloud after accounts_data schema change

Changed

• Rebuilt query builder for accounts_data with lazy, on-demand joins
• Database-agnostic SQL via IQueryBuilder expression API

Added

• DatabaseQueryException with operation context and safe API error text
• Integration test suite (make test-integration)
• Expanded unit tests for queries and error handling

Improved DB querying

v1.3.0

improve querying to use oc_accounts_data

Compatibility with NC30+

v1.2.0

rename all remaining occurances