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/server/src/server/agent/agent-manager.ts

@@ -352,14 +352,13 @@ export class AgentManager {
   recordUserMessage(
     agentId: string,
     text: string,
-    options?: { messageId?: string; raw?: unknown }
+    options?: { messageId?: string }
   ): void {
     const agent = this.requireAgent(agentId);
     const item: AgentTimelineItem = {
       type: "user_message",
       text,
       messageId: options?.messageId,
-      raw: options?.raw,
     };
     agent.updatedAt = new Date();
     agent.lastUserMessageAt = agent.updatedAt;