Add per-command sequence diagrams for hery

[jnbdz]

Adds the C4 dynamics level for hery: one sequence diagram per subcommand (entity dispatch, entity init/get/list/valid, query, compose, settings), embedded with prose on a new "hery Commands" page. Participants reuse the C3 component names so the diagrams zoom into the existing architecture view.

Spec-vs-code corrections applied while drawing (diagrams follow the code):

• hery entity get writes only the on-disk entity cache, never SQLite.
• No CLI command populates the SQLite entities table; hery query only reads it.
• hery settings reads env/types.go from the cwd, so it fails outside the source tree.
• The validate verb is valid; the diagram file keeps the validate basename.
• entity/schema/ is constructed but never invoked at runtime, so it appears in no diagram.