fix: remove unused providerState.ts file and clean up globalFileNames

- Removed unused src/core/task-persistence/providerState.ts file (fixes knip issue)
- Removed openAiNativeState entry from globalFileNames.ts
- Provider state is already handled internally in OpenAiNativeHandler

Author: daniel-lxs

src/core/task-persistence/providerState.ts

@@ -4,5 +4,4 @@ export const GlobalFileNames = {
 	mcpSettings: "mcp_settings.json",
 	customModes: "custom_modes.yaml",
 	taskMetadata: "task_metadata.json",
-	openAiNativeState: "openai_native_state.json",
 }