Add server-wide JSON output format support

[sam-at-luther]

Summary

This PR adds server-wide JSON output format support to all MCP tools. Users can now configure the output format via the OUTPUT_FORMAT environment variable to receive structured JSON responses instead of formatted markdown/text.

Changes

• ✅ Added OUTPUT_FORMAT environment variable (defaults to "markdown" for backward compatibility)
• ✅ Updated all 15 tools to support JSON output when OUTPUT_FORMAT="json"
• ✅ Added format_as_json() helper function with custom serializers for dates, decimals, and Oracle-specific types
• ✅ Added comprehensive test coverage for JSON output format
• ✅ Updated README with documentation for the new feature

Benefits

• Programmatic Integration: JSON output makes it easier to integrate MCP server responses into automated workflows, APIs, or other programs
• Structured Data: All tools now return consistent JSON structures that are easy to parse and process
• Backward Compatible: Default behavior unchanged - markdown format is still the default

Example JSON Output

When OUTPUT_FORMAT="json":

• run_sql_query returns: {"row_count": N, "columns": [...], "rows": [...]}
• get_table_schema returns: {"table_name": "...", "columns": [...], "relationships": {...}}
• get_table_constraints returns: {"table_name": "...", "constraints": [...]}
• And similarly for all other tools

Testing

• ✅ Added unit tests for JSON formatting with various data types
• ✅ Added integration tests for JSON output with actual database queries
• ✅ All existing tests pass (backward compatibility verified)

Documentation

• ✅ Updated README with OUTPUT_FORMAT configuration examples
• ✅ Added examples showing JSON output structure for different tools

[Copilot]

Pull Request Overview

This PR adds server-wide JSON output format support to all MCP tools. Users can now configure the output format via the OUTPUT_FORMAT environment variable to receive structured JSON responses instead of formatted markdown/text.

• Added OUTPUT_FORMAT environment variable with default value of "markdown" for backward compatibility
• Updated all 15 tools to support JSON output format when OUTPUT_FORMAT="json"
• Added comprehensive test coverage for JSON output format functionality

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/unit/test_json_output.py	New unit tests for JSON formatting with dates, decimals, nested structures, and null values
tests/unit/test_formatter_output.py	Added JSON output format tests for SQL query results and format_as_json helper
tests/integration/test_query_result_formatting.py	Added integration tests for JSON output with actual database queries
main.py	Updated all 15 tools to support JSON output format based on OUTPUT_FORMAT environment variable
db_context/schema/formatter.py	Added format_as_json helper function and JSON serialization support to format_sql_query_result
README.md	Updated documentation with OUTPUT_FORMAT configuration examples and JSON output structure

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