Add JSON output option for `werma st`

[ArLeyar]

Description

werma st currently outputs a human-readable status table. Adding a --json flag would make it easy to integrate Werma with other tools, scripts, and dashboards.

What needs to happen

1. Add --json flag to werma st command
2. Output task list as JSON array when flag is present
3. Include key fields: id, status, task_type, linear_issue_id, created_at, completed_at

Example

werma st --json | jq '.[] | select(.status == "running")'

Acceptance Criteria

• werma st --json outputs valid JSON
• JSON includes all relevant task fields
• Default (no flag) behavior unchanged