feat(cli): add --output-format=json flag for binary tool responses

[fuleinist]

Problem

When using the Chrome DevTools MCP CLI programmatically (e.g. in scripts or CI pipelines), binary tool responses like screenshots are returned as human-readable text summaries (e.g. Saved to /tmp/abc.png.) rather than structured machine-readable data. This makes it difficult to parse and use the actual file paths or base64 data in downstream tools.

Solution

Extend the existing --output-format=json flag (documented for list_pages) so it applies to all CLI commands — including those that return binary content (screenshot, performance_analyze_insight, etc.). When --output-format=json is set, the CLI should return a structured JSON object that includes:

• tool: the tool name
• filepath: (for file outputs) the absolute path to the saved file
• data or base64: (optionally) the raw base64 data
• metadata: any relevant metadata (dimensions, format, etc.)

Use case

Scripted regression tests or CI pipelines that call chrome-devtools take_screenshot --output-format=json and need to programmatically assert on the output file path or upload the resulting image — without parsing human-readable text.

References

• CLI docs already mention --output-format=json for list_pages (docs/cli.md)
• Binary tools currently return text like Saved to /tmp/abc.png. regardless of format flag

[OrKoN]

--output-format=json applied to all commands but it looks for take_screenshot it is missing the file path in the json structured output.