fix(cli): decode .env as UTF-8 to avoid GBK crash on Windows

Path.read_text() uses the system locale by default. On Windows CN/JP/KR
locales (GBK/CP932/CP949), reading a UTF-8 .env raises UnicodeDecodeError
as soon as it contains any non-ASCII byte (e.g. an em dash).

Pin encoding="utf-8" on every .env read in hermes_cli to match how the
rest of the codebase (load_dotenv at doctor.py:26) already decodes it.

Adds a regression test that monkeypatches Path.read_text to simulate a
GBK locale and asserts 'hermes doctor' no longer raises.

Refs #18637

hermes_cli/main.py

@@ -289,7 +289,7 @@ def _has_any_provider_configured() -> bool:
     env_file = get_env_path()
     if env_file.exists():
         try:
-            for line in env_file.read_text().splitlines():
+            for line in env_file.read_text(encoding="utf-8").splitlines():
                 line = line.strip()
                 if line.startswith("#") or "=" not in line:
                     continue