Add an AI agent for each component

Every component gets its own AI agent, on top of the shared agents and skills.

The component manifest is the source. Each agent carries the real variants, slots and props of its component, and still asks display_builder_ai for the details before it places anything, so the tool wins when the two disagree.

The agents ship as config entities in config/optional, so they install where the AI modules are present.

AI-Generated: Yes