feat: simplify subagent model configuration with model selector

Refactor subagent model configuration from nested modelConfig object to a simple model string field for better UX and clarity.

Changes:
- Replace modelConfig object with model string in SubagentConfig interface
- Add model-selection.ts utility for parsing and validating model selectors
- Support 'inherit' keyword and bare model IDs (e.g., 'glm-5', 'claude-sonnet-4-6')
- Maintain backward compatibility by parsing legacy modelConfig frontmatter
- Update validation to reject cross-provider authType-prefixed selectors
- Update SDK types (TypeScript and Java) to reflect new schema
- Add comprehensive tests for model selection and validation
- Update documentation with model selection examples

Breaking changes:
- modelConfig.frontmatter field deprecated in favor of model field
- Cross-provider model selectors (e.g., 'openai:gpt-4') not supported for subagents

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/cli/src/ui/components/subagents/manage/AgentViewerStep.tsx

@@ -40,6 +40,13 @@ export const AgentViewerStep = ({ selectedAgent }: AgentViewerStepProps) => {
           <Text>{toolsDisplay}</Text>
         </Box>
 
+        {agent.model && (
+          <Box>
+            <Text color={theme.text.primary}>{t('Model: ')}</Text>
+            <Text>{agent.model}</Text>
+          </Box>
+        )}
+
         {shouldShowColor(agent.color) && (
           <Box>
             <Text color={theme.text.primary}>{t('Color: ')}</Text>