Move <ui_state> snapshot injection out of respond_with_llm into a
cross-cutting on_before_process_frame handler on the UIWorker's LLM, so it
appends the current snapshot to the context the request is built from, just
before each inference. Injection is gated to the user-turn-initiating
inference so a tool-calling turn never stacks duplicate <ui_state> blocks;
respond_with_llm no longer injects manually.
Also drop the bridged parameter from UIWorker: there is no viable way to
bridge a UIWorker between workers — a shared, teed context would be polluted
by the injection, and per-worker turn detection off teed frames isn't
supported. Other workers keep their PipelineWorker bridging.
UIWorker is an LLMContextWorker that observes and drives a client GUI over the
RTVI UI channel: it stores accessibility snapshots, auto-injects <ui_state> at
the start of each respond job, dispatches client events to @on_ui_event
handlers, sends UI commands back to the client, and surfaces fan-out work as
cancellable task cards via user_job_group(). The optional ReplyToolMixin exposes
a bundled reply tool.
The prompt_guide parameter auto-appends the UI wire-format guide to the LLM's
system instruction (default UI_STATE_PROMPT_GUIDE; override with a string or
disable with None), so the LLM can parse the injected <ui_state> / <ui_event>
messages without the app concatenating the guide by hand.
