fix(windows): force UTF-8 encoding for all spawned child processes

- Set UTF-8 environment variables (PYTHONUTF8, PYTHONIOENCODING, LANG,
  LC_ALL) on all child processes via process.rs helpers
- Configure PTY terminals per shell flavor: chcp 65001 for cmd.exe,
  [Console]::OutputEncoding for PowerShell, LANG=C.UTF-8 for Git Bash
- Use /K and -NoExit for interactive shells to avoid nested processes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/process.rs

@@ -13,6 +13,7 @@ pub fn configure_std_command(command: &mut Command) -> &mut Command {
     {
         use std::os::windows::process::CommandExt;
         command.creation_flags(CREATE_NO_WINDOW);
+        set_utf8_env(command);
     }
 
     command
@@ -33,11 +34,47 @@ pub fn configure_tokio_command(
     #[cfg(windows)]
     {
         command.creation_flags(CREATE_NO_WINDOW);
+        set_utf8_env(command);
     }
 
     command
 }
 
+/// Hint child processes to produce UTF-8 output on Windows.
+///
+/// Sets environment variables recognised by common runtimes (Python, MSYS2/Git
+/// Bash, .NET console apps).  Not all programs honour these, but they cover the
+/// most frequent sources of mojibake in practice.
+#[cfg(windows)]
+fn set_utf8_env<C: SetEnv>(command: &mut C) {
+    // Python
+    command.env("PYTHONUTF8", "1");
+    command.env("PYTHONIOENCODING", "utf-8");
+    // MSYS2 / Git-for-Windows / POSIX-layer tools
+    command.env("LANG", "C.UTF-8");
+    command.env("LC_ALL", "C.UTF-8");
+}
+
+/// Abstraction over the `.env()` method shared by std and tokio Command types.
+#[cfg(windows)]
+trait SetEnv {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self;
+}
+
+#[cfg(windows)]
+impl SetEnv for Command {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self {
+        Command::env(self, key, val)
+    }
+}
+
+#[cfg(windows)]
+impl SetEnv for tokio::process::Command {
+    fn env(&mut self, key: &str, val: &str) -> &mut Self {
+        tokio::process::Command::env(self, key, val)
+    }
+}
+
 #[cfg(windows)]
 fn maybe_windows_cmd_shim(program: &OsStr) -> Option<OsString> {
     let path = Path::new(program);