Implements the doc command with subcommands for document management.

Subcommands: attach <node_id> <file> [-d description] Attach file to a node list [node_id] [--json] [--all] List documents show <doc_id> [--json] Show document details describe <doc_id> [description] Update description (stdin if no arg) open <doc_id> Open document in default app detach <doc_id> Soft-delete document gc [--dry-run] Remove orphaned files