test(sqlx): add config management tests (41 assertions)

Converted from src/config/config_test.sql

Implemented 7 config management tests:
- add_and_remove_multiple_indexes: Test adding/removing multiple indexes
- add_and_remove_indexes_from_multiple_tables: Multi-table index management
- add_and_modify_index: Modify index with options and cast
- add_index_with_existing_active_config: Pending config creation with active
- add_column_to_nonexistent_table_fails: Error handling for invalid tables
- add_and_remove_column: Column lifecycle management
- configuration_constraint_validation: Schema validation constraints

Key implementation details:
- Created config_tables.sql fixture with users and blah tables
- Helper function search_config_exists() for config state verification
- Note: Empty tables {} is VALID per constraints.sql (config_check_tables
  only validates field existence, not emptiness)

All 7 tests passing.

Author: tobyhede

tests/sqlx/fixtures/config_tables.sql

@@ -0,0 +1,16 @@
+-- Fixture for config tests
+-- Converted from src/config/config_test.sql lines 4-19
+
+DROP TABLE IF EXISTS users CASCADE;
+CREATE TABLE users (
+    id bigint GENERATED ALWAYS AS IDENTITY,
+    name eql_v2_encrypted,
+    PRIMARY KEY(id)
+);
+
+DROP TABLE IF EXISTS blah CASCADE;
+CREATE TABLE blah (
+    id bigint GENERATED ALWAYS AS IDENTITY,
+    vtha eql_v2_encrypted,
+    PRIMARY KEY(id)
+);