Remember server settings between sessions

- Server URLs are now saved to ~/.artdag/config.json when provided
- Subsequent commands use saved settings without needing --server/--l2
- Priority: CLI args > env vars > saved config > defaults
- Added 'artdag config' command to view/clear settings

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

.gitignore

@@ -2,3 +2,4 @@ __pycache__/
 *.py[cod]
 .venv/
 venv/
+.scripts