feat: smartlog — commit DAG with PR/CI status overlay

[erishforG]

Vision (v1.0: Ticket lifecycle complete)

Visualize all worktrees as a commit DAG with PR/CI status overlay in the terminal.

Proposal

parsec smartlog    # or: parsec sl

Example output

○ main
│
├─● CL-2283 Add rate limiting [PR #42 ✓ CI passed, ✓ approved]
│  ├─ a1b2c3d Implement rate limiter
│  └─ d4e5f6a Add tests
│
├─● CL-2284 Fix auth bug [PR #43 ● CI running]
│  └─ 7g8h9i0 Fix redirect
│
└─● CL-2291 API endpoints (no PR)
   └─ j1k2l3m WIP: initial scaffold

• Per-worktree commit display
• PR state (open/merged/draft), CI state (passed/failed/running), review state
• `--json` support
• Stack relationship visualization

Reference

• Sapling: `sl ssl` (super smartlog) — CI + PR review overlay
• git-branchless: `git sl` — commit DAG visualization

Milestone

v1.0