feat(terminal): add directory picker before launching Claude terminal (#1752)

* Add directory picker before launching Claude terminal

* fix(terminal): preserve cwd path and strip Windows verbatim prefix

- Stop trimming non-empty paths so directories with leading/trailing
  spaces on Unix are handled correctly
- Strip \\?\ extended-length prefix from canonicalized paths on Windows
  to prevent batch script cd failures

* fix(terminal): restore UNC paths when stripping Windows verbatim prefix

Handle \\?\UNC\server\share form separately from regular \\?\ prefix,
converting it back to \\server\share so network/WSL directory paths
remain valid in batch cd commands.

* fix(terminal): use pushd for UNC paths in Windows batch launcher

`cmd.exe` cannot set a UNC path (e.g. `\\wsl$\...`) as the current
directory via `cd /d`; it errors with "CMD does not support UNC paths
as current directories". Switch to `pushd` which temporarily maps the
UNC share to a drive letter.

Rename `build_windows_cd_command` → `build_windows_cwd_command` to
reflect the broader semantics. Extract `build_windows_cwd_command_str`
and `is_windows_unc_path` helpers for testability, and add unit tests
covering drive paths, UNC paths, and batch metacharacter escaping.

Also fix minor style issues: sort mod declarations alphabetically,
add missing EOF newline in lightweight.rs, add explicit type annotation
in streaming_responses test, and reformat tray menu builder chain.

src/App.tsx

@@ -648,7 +648,14 @@ function App() {
 
   const handleOpenTerminal = async (provider: Provider) => {
     try {
-      await providersApi.openTerminal(provider.id, activeApp);
+      const selectedDir = await settingsApi.pickDirectory();
+      if (!selectedDir) {
+        return;
+      }
+
+      await providersApi.openTerminal(provider.id, activeApp, {
+        cwd: selectedDir,
+      });
       toast.success(
         t("provider.terminalOpened", {
           defaultValue: "终端已打开",