Introduce client-side support for A2UI surfaces: new types, reducer, actions, UI and plumbing to record and show surface revision history. Adds A2uiThreadDock types and createDefaultA2uiDock, MAX_A2UI_REVISIONS_PER_SURFACE, and reducer helpers to record/focus/expand/set-active/mark-seen revisions. Wire into store: new a2uiDock actions, store helpers, thread runtime default, and thread event handling to seed docks from feed and record incoming ui_surface events. Replace inline surface card with a dock and compact history row (A2uiSurfaceDock, A2uiSurfaceHistoryRow, surfaceTitle), include a pop-out renderer and revision controls, and add unit tests for dock reducer behavior.
