Add description field to create_mode instructions (#5433)

* Add description field to create_mode instructions

- Include description field in optional but recommended fields list
- Add description field to YAML example with clear guidance
- Description field already exists in ModeConfig schema but was missing from instructions
- Provides short, human-readable description of what the mode does (1-2 sentences)

* Update description field guidance to 5 words instead of 1-2 sentences

- Changed description field guidance from '1-2 sentences' to '5 words'
- Updated YAML example to show concise 5-word description
- Addresses feedback from @mrubens in PR comment #3041823916

src/core/prompts/instructions/create-mode.ts

@@ -26,6 +26,7 @@ If asked to create a project mode, create it in .roomodes in the workspace root.
   * groups: Array of allowed tool groups (can be empty). Each group can be specified either as a string (e.g., "edit" to allow editing any file) or with file restrictions (e.g., ["edit", { fileRegex: "\\.md$", description: "Markdown files only" }] to only allow editing markdown files)
 
 - The following fields are optional but highly recommended:
+  * description: A short, human-readable description of what this mode does (5 words)
   * whenToUse: A clear description of when this mode should be selected and what types of tasks it's best suited for. This helps the Orchestrator mode make better decisions.
   * customInstructions: Additional instructions for how the mode should operate
 
@@ -36,6 +37,7 @@ Both files should follow this structure (in YAML format):
 customModes:
   - slug: designer  # Required: unique slug with lowercase letters, numbers, and hyphens
     name: Designer  # Required: mode display name
+    description: UI/UX design systems expert  # Optional but recommended: short description (5 words)
     roleDefinition: >-
       You are Roo, a UI/UX expert specializing in design systems and frontend development. Your expertise includes:
       - Creating and maintaining design systems
@@ -43,8 +45,8 @@ customModes:
       - Working with CSS, HTML, and modern frontend frameworks
       - Ensuring consistent user experiences across platforms  # Required: non-empty
     whenToUse: >-
-      Use this mode when creating or modifying UI components, implementing design systems, 
-      or ensuring responsive web interfaces. This mode is especially effective with CSS, 
+      Use this mode when creating or modifying UI components, implementing design systems,
+      or ensuring responsive web interfaces. This mode is especially effective with CSS,
       HTML, and modern frontend frameworks.  # Optional but recommended
     groups:  # Required: array of tool groups (can be empty)
       - read     # Read files group (read_file, fetch_instructions, search_files, list_files, list_code_definition_names)