[Compatibility] Power BI cannot connect to MatrixOne via MySQL connector

## Summary

Microsoft [Power BI](https://powerbi.microsoft.com/) **cannot connect to MatrixOne** via the MySQL connector (either Power BI Desktop or Power BI Service). This blocks critical customer requirements.

In an active customer POC, the original architecture document specified Power BI as the BI layer (connecting via MySQL connector to the data warehouse). Due to this compatibility gap, the POC currently uses a custom-patched Metabase as a workaround (see #24161). The customer's ideal production setup requires Power BI.

## Expected Behavior

Power BI Desktop should be able to:
1. Connect to MatrixOne using the MySQL connector (host, port, credentials)
2. Browse databases and tables in the Navigator pane
3. Import data or use DirectQuery mode
4. Execute DAX-generated SQL queries against MatrixOne

## Actual Behavior

Connection fails or metadata queries return unexpected results. Power BI's MySQL connector issues specific `information_schema` queries, session variable commands (`SET`), and metadata introspection queries that MatrixOne does not handle correctly.

## Impact

- Power BI is the **#1 enterprise BI tool** globally (Microsoft ecosystem)
- An active customer POC specifically requires Power BI for production deployment
- The POC already has a complete Power BI dashboard (7 pages, 50+ DAX measures) built against CSV data — migrating to a live MatrixOne connection is blocked by this issue
- Multiple enterprise customers are likely to require Power BI connectivity

## What Needs to Be Done

1. **Capture the exact queries** Power BI sends during connection setup and table browsing (MySQL connector protocol trace)
2. **Identify gaps** in MatrixOne's MySQL protocol layer:
- `information_schema` table/column metadata queries
- Session variable handling (`SET` commands Power BI sends)
- Data type mapping (Power BI expects specific MySQL type metadata)
- `SHOW` command output format
3. **Fix the protocol layer** so unmodified Power BI Desktop can connect
4. **Verify both modes**:
- Import mode (bulk data pull)
- DirectQuery mode (live SQL execution)
5. **Test with Power BI Service** (cloud) in addition to Desktop

## Suggested Approach

- Install Power BI Desktop (Windows)
- Attempt MySQL connector to a MatrixOne instance
- Use Wireshark or MySQL proxy to capture the failing protocol exchange
- Compare with a real MySQL 8.x server to identify the divergence

## Reference

- Metabase compatibility issue (same root cause family): #24161
- Customer architecture document specifies Power BI as target BI layer with 50+ DAX measures ready to migrate