fix: convert non-boolean additionalProperties to boolean in tool schemas

[lenanghai]

Summary

• Fixes non-boolean additionalProperties in generated tool schemas that break MCP clients like Claude Desktop and OpenAI Codex
• The ADK generates additionalProperties: {"type": "string"} for Dict[str, Any] type hints, but some clients expect a boolean value
• Adds a recursive _fix_additional_properties() function in the existing schema post-processing step in coordinator.py

Root Cause

Parameters typed as Dict[str, Any] (e.g., date_ranges, dimension_filter, metric_filter, order_bys in run_report) produce JSON Schema with additionalProperties: {"type": "string"} instead of additionalProperties: true. This causes:

• Claude Desktop: "No result received from client-side tool execution"
• OpenAI Codex: Failed to convert MCP tool: invalid type: map, expected a boolean

Test plan

• Verify run_report tool schema has additionalProperties: true (boolean) instead of {"type": "string"}
• Verify Claude Desktop can successfully call run_report
• Verify OpenAI Codex can discover and use run_report

Fixes #40

🤖 Generated with Claude Code

[google-cla]

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[matt-landers]

@lenanghai Thanks for your submission.

Can you sign the CLA here: https://cla.developers.google.com/