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/components/agent-stream-view.tsx

@@ -266,7 +266,7 @@ export function AgentStreamView({
             <ToolCall
               toolName={toolLabel}
               kind={data.kind}
-              args={data.raw}
+              args={undefined}
               result={data.result}
               error={data.error}
               status={data.status as "executing" | "completed" | "failed"}
@@ -565,17 +565,17 @@ function PermissionRequestCard({
   }, [request]);
 
   const editEntries = useMemo(
-    () => extractEditEntries(request.input, request.metadata, request.raw),
+    () => extractEditEntries(request.input, request.metadata),
     [request]
   );
 
   const readEntries = useMemo(
-    () => extractReadEntries(request.input, request.metadata, request.raw),
+    () => extractReadEntries(request.input, request.metadata),
     [request]
   );
 
   const commandDetails = useMemo(
-    () => extractCommandDetails(request.input, request.metadata, request.raw),
+    () => extractCommandDetails(request.input, request.metadata),
     [request]
   );