- Added the UI Agent Protocol to `pipecat.processors.frameworks.rtvi.models`:
  - Five first-class RTVI message types carry the wire format: `ui-event` (client → server), `ui-command` (server → client), `ui-snapshot` (client → server, accessibility tree), `ui-cancel-task` (client → server), and `ui-task` (server → client task lifecycle envelopes). Each ships a paired `*Data` / `*Message` pydantic model following the existing RTVI convention.
  - Built-in command payload models (`Toast`, `Navigate`, `ScrollTo`, `Highlight`, `Focus`, `Click`, `SetInputValue`, `SelectText`) ship alongside; matching default handlers live in `@pipecat-ai/client-react`.
  - The `RTVIProcessor` registers a new `on_ui_message` event handler that fires for inbound `ui-event` / `ui-snapshot` / `ui-cancel-task`.
  - Five new pipeline frames let pipeline observers and processors see UI traffic the same way they see other RTVI messages: `RTVIUICommandFrame` and `RTVIUITaskFrame` are pushed by downstream code to be wrapped by the observer into outbound `UICommandMessage` / `UITaskMessage` envelopes; `RTVIUIEventFrame`, `RTVIUISnapshotFrame`, and `RTVIUICancelTaskFrame` are pushed by the processor on inbound, alongside firing `on_ui_message`, mirroring the frame-and-event pattern used by `client-message`.
  - Bumps the RTVI `PROTOCOL_VERSION` from `1.2.0` to `1.3.0`.