perf: remove raw field from timeline items to reduce payload size

Remove the `raw` field that was duplicating provider data in timeline
items, reducing WebSocket payload sizes by 64-85%:
- session_state: ~320KB → ~48KB
- agent_stream_snapshot: ~320KB → ~114KB

Changes:
- Remove raw from AgentTimelineItem, AgentStreamEvent, AgentPermissionRequest
- Remove raw assignments from claude-agent.ts and codex-agent.ts
- Remove provider_event handling from stream.ts (only used for Codex raw)
- Update tests to reflect new behavior

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

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

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

@@ -38,7 +38,7 @@ const derivePendingPermissionKey = (agentId: string, request: AgentPermissionReq
     (typeof request.metadata?.id === "string" ? request.metadata.id : undefined) ||
     request.name ||
     request.title ||
-    `${request.kind}:${JSON.stringify(request.input ?? request.metadata ?? request.raw ?? {})}`;
+    `${request.kind}:${JSON.stringify(request.input ?? request.metadata ?? {})}`;
 
   return `${agentId}:${fallbackId}`;
 };