feat: US-008 - Inject callback into async tools in AgentLoop

- Update ToolRegistry.ExecuteWithContext to accept asyncCallback parameter
- Check if tool implements AsyncTool and set callback if provided
- Define asyncCallback in AgentLoop.runLLMIteration
- Callback uses bus.PublishOutbound to send async results to user
- Update Execute method to pass nil for backward compatibility
- Add debug logging for async callback injection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.ralph/prd.json

@@ -121,7 +121,7 @@
         "Typecheck passes"
       ],
       "priority": 8,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {