Add Apache Doris connector/runtime or document MySQL-compatible support

[intraq-dev-ai]

Connector gap

WrenAI README lists Apache Doris. IntraQ does not currently expose a Doris connector/runtime.

Evidence

WrenAI public README lists Apache Doris among supported data sources. IntraQ live SQL execution currently supports PostgreSQL, MySQL/MariaDB, SQL Server, Databricks, and ClickHouse.

Acceptance criteria

• Add Apache Doris as a selectable connector, or document a compatible path if it is intentionally covered through MySQL protocol.
• Support schema discovery, query preview, SQL Editor execution, Analyzer, and Dashboard Builder.
• Add tests for connection handling, type normalization, limits, and dialect differences.