refactor(claude-desktop): lock route IDs to sonnet/opus/haiku roles

Adapt to Claude Desktop 1.6259.1+ fail-all validation which only
accepts claude-(sonnet|opus|haiku)-* route IDs. Branded model names
(DeepSeek, Kimi, GLM, etc.) now live in a new labelOverride field
instead of being embedded in route IDs.

- Backend auto-repairs legacy unsafe routes to the next free
  sonnet/opus/haiku slot instead of erroring
- Frontend swaps the free-form route input for a role dropdown plus
  menu display name field
- Add CLAUDE_DESKTOP_ROLE_ROUTE_IDS as the single source of truth
  for role-to-route mapping; presets and form both consume it
- Drop the dead displayName alias on ClaudeDesktopModelRoute and the
  ineffective /v1/models display_name injection (UI ignores it)
- Update i18n (en/ja/zh) and form focus test for the new fields

src-tauri/src/provider.rs

@@ -230,6 +230,9 @@ pub enum ClaudeDesktopMode {
 pub struct ClaudeDesktopModelRoute {
     /// 真实上游模型名，只保存在 CC Switch 内部，不写入 Claude Desktop profile。
     pub model: String,
+    /// Claude Desktop 模型菜单显示名；写入 profile 的 `labelOverride`。
+    #[serde(rename = "labelOverride", skip_serializing_if = "Option::is_none")]
+    pub label_override: Option<String>,
     /// Claude Desktop 3P 识别的 1M 上下文能力标记。
     #[serde(rename = "supports1m", skip_serializing_if = "Option::is_none")]
     pub supports_1m: Option<bool>,