Adds a new CLI command `archivebox pluginmap` that displays:
- ASCII art diagrams of all core state machines (Crawl, Snapshot,
ArchiveResult, Binary)
- Lists all auto-detected on_Modelname_xyz hooks grouped by model/event
- Shows hook execution order (step 0-9), plugin name, and background status
Usage:
archivebox pluginmap # Show all diagrams and hooks
archivebox pluginmap -m Snapshot # Filter to specific model
archivebox pluginmap -a # Include disabled plugins
archivebox pluginmap -q # Output JSON only
