[ML 0.1/UI.04.5] - Wire footer button (lazy load) to legacy action

[rafaeltonholo]

Blocked by

• [ML 0.1/UI.04.2] - Implement legacy message list loading bridge #10775

Description

Wire the footer button in the Compose message list to the legacy "load more messages" action. This includes adding OnFooterClick event handling in the state machine and emitting effects consumed by the legacy fragment.

Acceptance Criteria

• MessageListEvent.OnFooterClick is dispatched from the renderer.
• State machine handles the event and emits the appropriate MessageListEffect.
• MessageListFragment consumes the effect and triggers the legacy load-more action.
• Footer updates are propagated from legacy to the Compose UI.