feat(skills): add librefang-workflow skill for workflow management

[DaBlitzStein]

Summary

There is no skill in the registry for managing LibreFang workflows (create, list, run, inspect runs, delete). Agents that need workflow capabilities currently have librefang-workflow in their skills list, but the skill doesn't exist — it resolves to nothing at runtime.

Motivation

LibreFang has a full workflow engine (crates/librefang-kernel/src/workflow.rs) with API endpoints for CRUD operations, step execution, and run history. Agents should be able to discover and use these capabilities through a skill that provides:

• Guidance on workflow_run, workflow_list, workflow_create tools
• Best practices for multi-step workflows (error handling, human-in-the-loop steps)
• Examples of chaining agents, conditions, and parallel execution
• Context about the workflow editor in the dashboard

Current state

• Workflow tools exist as builtins (workflow_run, workflow_list, etc.)
• Dashboard has a workflow editor with visual step builder
• No skill provides the prompt context to help agents use workflows effectively
• librefang-workflow is referenced in agent configs but doesn't resolve

Suggested scope

A librefang-workflow skill with a SKILL.md that describes available workflow tools, their parameters, and usage patterns — similar to how git-expert provides context for git operations.