List Specs

Show all specs grouped by status.

1. If .specs/registry.md does not exist, report "No specs yet" and suggest running /specmint-core:forge.
2. Read .specs/registry.md.
3. For each spec row, read .specs/<id>/SPEC.md to compute accurate task counts ([x] and total), current phase, and current task marker.
4. Present grouped by status in this order: active, paused, completed, archived. If a registry row points to a missing SPEC.md, show it under the right status with (SPEC.md missing) and continue.

Active:
  → auth-system: User Auth System (5/12 tasks, Phase 2) [high]

Paused:
  ⏸ api-refactor: API Refactoring (2/8 tasks, Phase 1) [medium]
  ⏸ dark-mode: Dark Mode Support (0/6 tasks, not started) [low]

Completed:
  ✓ ci-pipeline: CI Pipeline Setup (8/8 tasks) [high]

If there are no rows after the table header, suggest running /specmint-core:forge to create one.