Implement ClickHouse dialect

[RAprogramm]

Problem

ClickHouse dialect declared but not implemented. Current state:

• Placeholder exists in code
• Using it produces compile_error
• Users expect it to work

Why it matters

• Promised feature not delivered
• ClickHouse popular for analytics
• Different SQL syntax needs handling
• Expands use cases

Acceptance criteria

• Working ClickHouse implementation
• Proper placeholder syntax
• Handle ClickHouse-specific types
• Integration tests