feat: add live progress during orchestrator plan generation

New SSE event orchestrator:planProgress streams phase/detail updates
from the planner to the frontend in real-time. The panel now shows
a scrollable log of planning steps instead of just "Generating plan..."

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/web/sse-events.ts

@@ -296,6 +296,8 @@ export const HookTaskCompleted = 'hook:task_completed' as const;
 
 /** Orchestrator state machine transitioned. */
 export const OrchestratorStateChanged = 'orchestrator:stateChanged' as const;
+/** Orchestrator plan generation progress update. */
+export const OrchestratorPlanProgress = 'orchestrator:planProgress' as const;
 /** Orchestrator plan generated and ready for approval. */
 export const OrchestratorPlanReady = 'orchestrator:planReady' as const;
 /** Orchestrator phase started executing. */
@@ -468,6 +470,7 @@ export const SseEvent = {
 
   // Orchestrator
   OrchestratorStateChanged,
+  OrchestratorPlanProgress,
   OrchestratorPlanReady,
   OrchestratorPhaseStarted,
   OrchestratorPhaseCompleted,