feat: Art DAG CLI client

- artdag.py CLI for L1 server interaction
- run: start rendering jobs
- runs: list all runs
- status: check run status
- cache/view: manage cached content (pipe to mpv with -o -)
- assets: list known assets
- import: add files to cache

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,4 @@
+__pycache__/
+*.py[cod]
+.venv/
+venv/