feat: add status command change proposal

[TabishB]

Summary

This PR adds a change proposal for implementing an openspec status command that will provide visibility into the state of OpenSpec changes.

What This PR Contains

This is a change proposal only - no implementation yet. The proposal includes:

• proposal.md - Explains why we need the status command
• tasks.md - Implementation checklist with 7 task groups
• design.md - Technical architecture and parsing strategy
• specs/cli-status/ - Future state specifications

Proposed Feature

The status command would provide visibility into:

• Changes ready to archive (all tasks complete)
• Changes in progress (some tasks incomplete)
• Recently archived changes

Proposed Output Example

OpenSpec Status Report
═══════════════════════

Ready to Archive (2):
  ✓ feature-auth           15/15 tasks   3 days old
  ✓ fix-payment-bug        8/8 tasks     1 day old

In Progress (3):
  ⚠ add-user-profile       12/20 tasks   2 days old
  ⚠ refactor-api          3/10 tasks    5 days old

Key Design Decisions

• Robust task parsing: Would handle multiple checkbox formats ([x], [X], [✓])
• Context-aware: Would skip false positives in code blocks
• Multiple output formats: Summary, detailed, and JSON views
• Workflow integration: Complements the archive command proposal

Next Steps

Once this proposal is approved:

1. Implementation will follow the tasks outlined in tasks.md
2. The status command will be built alongside or before the archive command
3. Both commands will share task parsing utilities

Review Checklist

• Review the proposed command interface
• Check if the task parsing strategy is robust enough
• Validate the proposed output formats
• Confirm the workflow integration makes sense