feat: add "Requires Attention" agent grouping feature

Implement a new UI section that surfaces agents requiring user attention at the top of the agent list. This includes agents that are running, have pending permissions, or have errors.

**Backend changes:**
- Add `requiresAttention` field to agent projections and SDK types
- Implement logic in AgentManager to detect attention states (running, pending permissions, errors)
- Add WebSocket message handler to notify clients of attention state changes
- Update session state to include attention tracking

**Frontend changes:**
- Add "REQUIRES ATTENTION" section in agent-list component with visual prominence
- Update useAggregatedAgents hook to expose `requiresAttention` agents
- Enhance session store to track and update attention states
- Add real-time updates via WebSocket for attention state changes
- Update type definitions across agent directory and stream types

Verified working via Playwright MCP testing on localhost:8081.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

packages/app/src/contexts/session-context.tsx

@@ -114,6 +114,7 @@ function normalizeAgentSnapshot(snapshot: AgentSnapshotPayload, serverId: string
   const createdAt = new Date(snapshot.createdAt);
   const updatedAt = new Date(snapshot.updatedAt);
   const lastUserMessageAt = snapshot.lastUserMessageAt ? new Date(snapshot.lastUserMessageAt) : null;
+  const attentionTimestamp = snapshot.attentionTimestamp ? new Date(snapshot.attentionTimestamp) : null;
   return {
     serverId,
     id: snapshot.id,
@@ -134,6 +135,9 @@ function normalizeAgentSnapshot(snapshot: AgentSnapshotPayload, serverId: string
     title: snapshot.title ?? null,
     cwd: snapshot.cwd,
     model: snapshot.model ?? null,
+    requiresAttention: snapshot.requiresAttention ?? false,
+    attentionReason: snapshot.attentionReason ?? null,
+    attentionTimestamp,
   };
 }