feat: add --json output mode

[nkar123412-hub]

Implemented the requested --json flag to allow the tool to output project context in a structured JSON format.

Changes:

• Added argument to CLI.
• Implemented data collection into a dictionary for flexible output.
• Added a for automated verification.

Verification:

• JSON output is valid and contains all required fields.
• Default text output remains unchanged.
• Graceful failure for non-git repositories is preserved.
• All tests passed.