Implement an init subcommand that scaffolds different workflows

[willkg]

Add an init subcommand that scaffolds different workflows.

• GHA workflow into a repository to publish markdown files (markfluence update)
  • Scope / open questions:
    • Exactly which workflow to write (trigger, steps, how markfluence is installed, how creds are provided via secrets).
    • Idempotency / not clobbering an existing workflow.
• markfluence.yaml file to denote project root
• maybe Claude bits to make markfluence parts of the project clearer