[Feature] Add JSON output format for pipeline integration

[AdvancingTitans]

Background

All current commands output formatted tables (using rich). Users running automated pipelines, cron jobs, or shell scripts need machine-readable output.

Requirements

• Global flag --json for all subcommands
• Example: young indices --json outputs JSON array instead of table
• Should be pipe-friendly: young a --zt --json | jq '.[] | .code'

Suggested implementation

• Add --json to the root group in cli.py
• When set, skip rich Table rendering and call json.dumps() on the raw data dict
• Each subcommand should already have structured data before rendering, so this is mostly a render-layer fork

Acceptance

• young indices --json outputs valid JSON
• young a --zt --json outputs valid JSON
• young global --json outputs valid JSON
• Tests verify JSON is parseable
• README updated with pipeline examples

For

• Python users who like click
• Anyone using A-share data in shell pipelines

Easy first PR!

[dhyan95]

Hey @AdvancingTitans! I'm a graduate student with a strong background in Python data processing and automation pipelines. I'd love to implement this global --json flag to make the tool pipe-friendly for automated workflows.

I will handle the click parameter parsing, fork the rendering layer to intercept the structured data before it hits the rich tables, add unit tests to verify the outputs are valid JSON, and update the README with a pipeline example using jq.

Could you please assign this issue to me? I'm ready to fork and get to work!