Add Microsoft SQL Server (MSSQL) database support

[mikenikles]

Summary

• Add custom Rust backend using tiberius crate for native MSSQL connections
• Implement MSSQL-specific commands: mssql_connect, mssql_disconnect, mssql_query, mssql_execute
• Add MssqlAdapter with SQL Server-specific schema discovery queries
• Support SQL Server pagination using OFFSET FETCH syntax
• Handle MSSQL identifier quoting with square brackets [name]
• Integrate with existing connection manager, query execution, and schema tabs
• Support SSH tunneling for MSSQL connections
• Add TLS encryption support with configurable certificate trust

Test plan

• Test connecting to a SQL Server database
• Test executing SELECT queries with pagination
• Test executing INSERT/UPDATE/DELETE queries
• Test schema discovery (tables, columns, indexes, foreign keys)
• Test SSH tunnel connections to MSSQL
• Verify connection status indicators in header and sidebar

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