fix: use json-stream-stringify for pretty-printing MCP config files

[roomote]

This PR attempts to address Issue #9862 by implementing the suggestion from @Michaelzag to use json-stream-stringify instead of the built-in JSON.stringify for pretty-printing MCP configuration files.

Problem

The safeWriteJson() utility was using stream-json which only outputs compact/minified JSON, making configuration files like .roo/mcp.json difficult to read and manually edit after being modified through the UI.

Solution

• Replaced stream-json with json-stream-stringify library which supports streaming pretty-printing
• Added a prettyPrint option to the safeWriteJson() function
• Updated all MCP configuration write calls to use { prettyPrint: true }
• Maintains true streaming throughout the entire process without materializing the full JSON string in memory

Changes

• Modified src/utils/safeWriteJson.ts to use JsonStreamStringify with optional indentation
• Updated src/services/mcp/McpHub.ts to pass { prettyPrint: true } for all config writes
• Updated src/core/webview/webviewMessageHandler.ts to use pretty-printing for project MCP settings
• Added json-stream-stringify as a dependency

Benefits

• Configuration files maintain human-readable formatting after UI modifications
• Memory efficient - still uses streaming for large files
• Backward compatible - existing code continues to work

Testing

• All existing tests pass
• The safeWriteJson test suite runs successfully

Fixes #9862

Feedback and guidance are welcome!

[roomote]

Rooviewer   See task on Roo Cloud

Review completed. Found 1 issue that should be addressed before merging.

Issues Found

• Undefined handling removed: The original implementation converted undefined values to null for valid JSON serialization. The new implementation passes undefined directly to JsonStreamStringify, which will serialize it as the string "undefined" instead of null, breaking the existing contract.

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

The original implementation had special handling for undefined values, converting them to null before serialization. This new implementation passes undefined directly to JsonStreamStringify, which will serialize it as the string "undefined" rather than null. This breaks the existing contract where undefined root values were written as valid JSON (null). Consider adding back the undefined check: const dataToWrite = data === undefined ? null : data before passing to JsonStreamStringify.

_{Fix it with Roo Code or mention @roomote and request a fix.}