fix MCP list_databases output schema and params context handling

[lucarizzo03]

Summary

• Ensure list_databases returns only list output on success
• Raise MCP tool errors instead of returning schema-incompatible error dicts
• Add defensive handling for missing ctx.params in MCP execution paths

Validation

• Reproduced original schema validation failure
• Retested list_databases after fix; now returns database names without output schema error

[github-actions]

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[lucarizzo03]

I have read the CLA Document and I hereby sign the CLA

[StpMax]

@lucarizzo03 Thank you for your contribution. Unfortunately, I have to close your PR. The MCP server has already been significantly reworked in the upcoming update, which is located in this branch.