**Refactor:** Restructure server package to streamline imports and improve file organization

- Moved `providers`, `services`, `models`, `lib`, and related files to `src` directory within `server` package.
- Adjusted imports across the codebase to reflect the new paths.
- Renamed several `.ts` files for consistency.
- Introduced an `index.ts` in the `ai/providers` package to export all providers.

This improves maintainability and aligns with the project's updated directory structure.

packages/server/src/models/O1Message.ts

@@ -0,0 +1,20 @@
+import { types } from 'mobx-state-tree';
+
+export default types
+  .model('O1Message', {
+    role: types.enumeration(['user', 'assistant', 'system']),
+    content: types.array(
+      types.model({
+        type: types.string,
+        text: types.string,
+      }),
+    ),
+  })
+  .actions(self => ({
+    setContent(newContent: string, contentType: string = 'text') {
+      self.content = [{ type: contentType, text: newContent }];
+    },
+    append(newContent: string, contentType: string = 'text') {
+      self.content.push({ type: contentType, text: newContent });
+    },
+  }));