feat: add model selection for AI agents (claude, codex, gemini)

Add a new ModelSelector component that allows users to choose specific model variants for different AI agents. This includes:
- ModelSelector UI component with agent-specific model options
- Model parameter propagation through API, RPC, and spawning layers
- Support for auto model selection (default behavior)
- Localization strings for English and Chinese
- Type definitions for model options per agent

cli/src/modules/common/rpcTypes.ts

@@ -4,6 +4,7 @@ export interface SpawnSessionOptions {
     sessionId?: string
     approvedNewDirectoryCreation?: boolean
     agent?: 'claude' | 'codex' | 'gemini'
+    model?: string
     yolo?: boolean
     token?: string
     sessionType?: 'simple' | 'worktree'