fix(config): preserve original .env file mode in remove_env_value too (#43349)

#33699 fixed save_env_value so an operator-set .env mode (e.g. 0640 on a
Docker bind-mount) survives a config write instead of being re-tightened
to 0600 by the unconditional _secure_file() call. The sibling
remove_env_value() had the identical bug: it restores original_mode and
then unconditionally called _secure_file(env_path), clobbering the mode
back to 0600 on every `hermes config remove KEY`.

Apply the same fix: move _secure_file() into the else branch so it only
runs when no original mode was captured (a freshly created .env still
gets 0600 hardening; existing operator-set modes survive).

Added test_remove_env_value_preserves_existing_file_mode_on_posix, which
fails on the unfixed remove path (expected 0o640, got 0o600) and passes
with the fix.

hermes_cli/config.py

@@ -5808,18 +5808,22 @@ def remove_env_value(key: str) -> bool:
                 f.flush()
                 os.fsync(f.fileno())
             atomic_replace(tmp_path, env_path)
+            # Preserve the original file mode (e.g. 0640 for Docker volume
+            # mounts) instead of letting _secure_file unconditionally tighten
+            # to 0600. Mirrors save_env_value().
             if original_mode is not None:
                 try:
                     os.chmod(env_path, original_mode)
                 except OSError:
                     pass
+            else:
+                _secure_file(env_path)
         except BaseException:
             try:
                 os.unlink(tmp_path)
             except OSError:
                 pass
             raise
-        _secure_file(env_path)
 
     os.environ.pop(key, None)
     invalidate_env_cache()