refactor: Move to agent architecture

sources/agents/openai_chat_completions.toml

@@ -0,0 +1,16 @@
+schema_version = 1
+
+extends     = "OpenAI Base Chat"
+name        = "OpenAI Chat Completions"
+description = "OpenAI GPT-4o — coding chat via Chat Completions."
+
+model           = "gpt-4o"
+enable_tools    = true
+enable_thinking = true
+tags            = ["chat", "openai", "cloud"]
+
+system_prompt = """{{ read_file(":/roles/qt-cpp-developer.md") }}"""
+
+[body]
+max_tokens  = 8192
+temperature = 0.7