sec(editor): add confirmation modal for destructive DDL and DML operations (#608)

[ZhuchkaTriplesix]

Summary

Implements a safety inspection layer and confirmation dialog for destructive SQL statements (DROP DATABASE, DROP SCHEMA, DROP TABLE, DROP VIEW, DROP MATERIALIZED VIEW, TRUNCATE TABLE, and unconditional DELETE FROM) before executing queries in PostgreSQL, MySQL, and SQLite workspaces.

Changes

1. Destructive SQL Detector (lib/core/database/destructive_sql_detector.dart):
   • Strips SQL comments (--, /* */) and single/dollar-quoted strings to prevent false positives.
   • Splits queries on semicolons and matches destructive DDL and DML patterns.
   • Assigns severity risk levels (CRITICAL, HIGH, MEDIUM).
2. Confirmation Modal Dialog (lib/features/main_screen/destructive_query_dialog.dart):
   • Displays risk badges, target object descriptions, SQL script preview, copy button, and an acknowledgment checkbox to prevent accidental confirms.
3. Workspaces Integration:
   • Integrated check into _execute() in PostgresSqlWorkspace, MysqlSqlWorkspace, and SqliteSqlWorkspace.
4. App Settings & Preferences:
   • Added AppSettings.confirmDestructiveOperations (default: true).
   • Added preference toggle in PreferencesDialog under the SQL editor section.
5. Testing:
   • Unit tests in test/core/database/destructive_sql_detector_test.dart.
   • Widget tests in test/features/main_screen/destructive_query_dialog_test.dart.

Closes #608