feat: add OpenAI responses wrapper

PROJECT_STATE.md

@@ -7,11 +7,11 @@ ChatGPT MCP Server
 ## Status
 
 Planning complete.
-Phase 0 complete. Phase 1 in progress.
+Phase 0 complete. Phase 1 complete. Phase 2 in progress.
 
 ## Current Phase
 
-Phase 1 - Core Utilities
+Phase 2 - OpenAI Integration
 
 ## Completed Tasks
 
@@ -21,7 +21,13 @@ Phase 1 - Core Utilities
 - Task 1.2 — Secret redaction utility (`src/utils/redact.js`) ✅
 - Task 1.3 — Context budget utility (`src/utils/context-budget.js`) ✅
 - Task 1.4 — Safe logging helper (`src/utils/logging.js`) ✅
+- Task 2.1 — OpenAI client wrapper (`src/openai/client.js`) ✅
+- Task 2.2 — Response builder (`src/openai/responses.js`) ✅
 
 ## Next Phase
 
 Phase 2 - OpenAI Integration
+
+## Next Pending Task
+
+Task 2.3 — Error handling and edge cases for OpenAI integration