Support configurable ClickHouse settings per source connection

[mr-karan]

Problem

Currently, ClickHouse connection settings are hardcoded. Users cannot configure per-source query settings.

Proposed Solution

Allow configuring common ClickHouse settings via driver connections, per source:

• max_execution_time
• max_result_rows / max_result_bytes
• max_rows_to_read / max_bytes_to_read
• readonly mode
• result_overflow_mode (throw/break)

Implementation

• Add settings field to source connection config
• Apply settings per-query via ClickHouse client
• Expose in source creation/edit UI

Use Cases

• Different timeout limits for different sources
• Hard caps on result sizes for shared sources
• Read-only enforcement at connection level