docs: add groups to modelspecs

pages/docs/configuration/librechat_yaml/object_structure/model_specs.mdx

@@ -199,11 +199,75 @@ URL or a predefined endpoint name for the model's icon.
   ]}
 />
 
-**Description:**  
+**Description:**
 A brief description of the model and its intended use or role, shown in the header dropdown menu.
 
 ---
 
+### group
+
+<OptionTable
+  options={[
+    ['group', 'String', 'Optional group name for organizing model specs in the UI selector. Controls where the spec appears in the menu hierarchy.', 'No default. Optional.'],
+  ]}
+/>
+
+**Description:**
+Optional group name for organizing model specs in the UI selector. The `group` field provides flexible control over how model specs are organized:
+
+- **If `group` matches an endpoint name** (e.g., `"openAI"`, `"groq"`): The model spec appears nested under that endpoint in the selector menu
+- **If `group` is a custom name** (doesn't match any endpoint): Creates a separate collapsible section with that name
+- **If `group` is omitted**: The model spec appears as a standalone item at the top level
+
+This feature is particularly useful when you want to add descriptions to models without losing the organizational structure of the selector menu.
+
+**Example:**
+
+```yaml filename="modelSpecs with group field examples"
+modelSpecs:
+  list:
+    # Example 1: Nested under an endpoint
+    # When group matches an endpoint name, the spec appears under that endpoint
+    - name: "gpt-4o-optimized"
+      label: "GPT-4 Optimized"
+      description: "Most capable GPT-4 model with multimodal support"
+      group: "openAI"  # Appears nested under the OpenAI endpoint
+      preset:
+        endpoint: "openAI"
+        model: "gpt-4o"
+
+    # Example 2: Custom group section
+    # When group is a custom name, it creates a separate collapsible section
+    - name: "coding-assistant"
+      label: "Coding Assistant"
+      description: "Specialized for coding tasks"
+      group: "my-assistants"  # Creates a custom "my-assistants" section
+      preset:
+        endpoint: "openAI"
+        model: "gpt-4o"
+
+    # Multiple specs with the same group name are grouped together
+    - name: "writing-assistant"
+      label: "Writing Assistant"
+      description: "Specialized for creative writing"
+      group: "my-assistants"  # Grouped together with coding-assistant
+      preset:
+        endpoint: "anthropic"
+        model: "claude-sonnet-4"
+
+    # Example 3: Standalone (no group)
+    # When group is omitted, the spec appears at the top level
+    - name: "general-assistant"
+      label: "General Assistant"
+      description: "General purpose assistant"
+      # No group field - appears as standalone item at top level
+      preset:
+        endpoint: "openAI"
+        model: "gpt-4o-mini"
+```
+
+---
+
 ### showIconInMenu
 
 <OptionTable