feat: real-time activity indicator in log panel

- New WsMessage::ActivityUpdate for live status broadcasting
- Shows current activity at bottom of log: LLM calls, tool execution, user approval
- Activity bar with spinner, auto-clears on workflow completion
- Status badge with pulse animation in log header

web/src/ws.ts

@@ -40,12 +40,18 @@ export interface WsLlmCallLog {
   entry: import('./types').LlmCallLogEntry
 }
 
+export interface WsActivityUpdate {
+  type: 'ActivityUpdate'
+  workflow_id: string
+  activity: string
+}
+
 export interface WsError {
   type: 'Error'
   message: string
 }
 
-export type WsMessage = WsPlanUpdate | WsStepStatusUpdate | WsWorkflowStatusUpdate | WsRequirementUpdate | WsReportReady | WsProjectUpdate | WsLlmCallLog | WsError
+export type WsMessage = WsPlanUpdate | WsStepStatusUpdate | WsWorkflowStatusUpdate | WsRequirementUpdate | WsReportReady | WsProjectUpdate | WsLlmCallLog | WsActivityUpdate | WsError
 
 export type WsHandler = (msg: WsMessage) => void