refactor(claude-desktop): trim duplication in proxy and switch flows

- services/proxy.rs: collapse 10 repeated `OpenCode | OpenClaw | Hermes |
  ClaudeDesktop` match arms into `_` fallthroughs.
- claude_desktop_config.rs: extract a `with_rollback` closure shared by
  apply_provider_to_paths and restore_official_at_paths.
- useProviderActions.ts: replace the triple-nested ternary picking the
  switch-success toast message with a flat let/if/else block.

Net -36 lines. No behavior change; cargo test and pnpm typecheck pass.

src/hooks/useProviderActions.ts

@@ -227,26 +227,21 @@ export function useProviderActions(
 
         // 若已弹过 proxyRequired 警告则不再弹 success
         if (!proxyRequiredReason) {
-          // OpenCode/OpenClaw: show "added to config" message instead of "switched"
-          const isMultiProviderApp =
-            activeApp === "opencode" || activeApp === "openclaw";
-          const messageKey =
-            activeApp === "claude-desktop"
-              ? provider.meta?.claudeDesktopMode === "proxy"
-                ? "notifications.claudeDesktopProxyRestartRequired"
-                : "notifications.claudeDesktopRestartRequired"
-              : isMultiProviderApp
-                ? "notifications.addToConfigSuccess"
-                : "notifications.switchSuccess";
-          const defaultMessage =
-            activeApp === "claude-desktop"
-              ? provider.meta?.claudeDesktopMode === "proxy"
-                ? "切换成功，请保持 CC Switch 运行，并重启 Claude Desktop 后生效"
-                : "切换成功，重启 Claude Desktop 后生效"
-              : isMultiProviderApp
-                ? "已添加到配置"
-                : "切换成功！";
-
+          let messageKey = "notifications.switchSuccess";
+          let defaultMessage = "切换成功！";
+          if (activeApp === "claude-desktop") {
+            if (provider.meta?.claudeDesktopMode === "proxy") {
+              messageKey = "notifications.claudeDesktopProxyRestartRequired";
+              defaultMessage =
+                "切换成功，请保持 CC Switch 运行，并重启 Claude Desktop 后生效";
+            } else {
+              messageKey = "notifications.claudeDesktopRestartRequired";
+              defaultMessage = "切换成功，重启 Claude Desktop 后生效";
+            }
+          } else if (activeApp === "opencode" || activeApp === "openclaw") {
+            messageKey = "notifications.addToConfigSuccess";
+            defaultMessage = "已添加到配置";
+          }
           toast.success(t(messageKey, { defaultValue: defaultMessage }), {
             closeButton: true,
           });