Implement UI enhancements, change password settings, theme toggle, and custom grid size slider

frontend/src/lib/api.ts

@@ -137,6 +137,14 @@ class ApiClient {
     this.clearTokens();
   }
 
+  async changePassword(oldPassword: string, newPassword: string) {
+    const res = await this.request('/api/auth/password', {
+      method: 'PUT',
+      body: { old_password: oldPassword, new_password: newPassword },
+    });
+    return res.json();
+  }
+
   // --- Files ---
   async listDirectory(path: string = '.') {
     const res = await this.request(`/api/files/?path=${encodeURIComponent(path)}`);