fix: throw error when Slack events API returns success: false

Ensure the Slack events endpoint never returns an HTTP 200 with success: false in the response body. Any failed event processing will now properly throw an error and return an appropriate error status code.

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

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

apps/server/src/api/v2/slack/events.ts

@@ -147,6 +147,12 @@ export async function handleSlackEventsEndpoint(c: Context) {
   try {
     // Process the event
     const response = await eventsHandler(payload);
+    
+    // Ensure we never return success: false without throwing
+    if (!response.success) {
+      throw new Error('Event processing failed');
+    }
+    
     return c.json(response);
   } catch (error) {
     // Handle authentication errors