feat(observability): add Chat view and thread query interfaces

- Add GetTraceChat/GetThreadChat/GetThreadStat IDL definitions
- Add ChatMessage struct with message_type and span fields
- Implement ChatProcessor for extracting last user message from model span input
- Support Standard ChatCompletion and Responses API formats
- Add service layer implementations with chat processor integration
- Add application handler layer with permission validation
- Add ChatMessagesDO2DTO convertor function
- Add unit tests for ChatProcessor

Author: kidkidkid

.gitignore

@@ -21,6 +21,9 @@ go.work.sum
 # the result of the go build
 output/
 
+# local tool binaries
+backend/bin/
+
 # Files generated by IDEs
 .idea/
 *.iml