Implement MongoDB dialect #24
Description
Problem
MongoDB dialect declared but not implemented. Current state:
- Placeholder exists in code
- Using it produces compile_error
- Document databases have different patterns
Why it matters
- Promised feature not delivered
- MongoDB widely used
- Document model differs from relational
- Expands target audience
Acceptance criteria
- Working MongoDB implementation
- Handle document structure
- Proper BSON type handling
- Integration tests