fix: add explicit UTF-8 encoding to _op_whoami subprocess call (#53428)

PR #55339 adds encoding='utf-8', errors='replace' to 26 subprocess.run(text=True)
call sites across the codebase. The triage review (thanks @alt-glitch) diffed
this PR against #55339 and found that 5 of the 6 originally-touched call sites
are already covered there byte-identically:

- hermes_cli/main.py::_probe_container
- hermes_cli/setup.py SSH probe
- tools/tts_tool.py::_generate_neutts
- tools/transcription_tools.py::_prepare_local_audio
- tools/transcription_tools.py::_transcribe_local_command (both branches)

The one genuinely net-new site — hermes_cli/onepassword_secrets_cli.py::_op_whoami
(the 1Password op CLI whoami probe) — is NOT in #55339 and is fixed here.

Without explicit encoding=, text=True decodes child output with
locale.getpreferredencoding(False) — cp936 on Chinese Windows — which crashes
_readerthread on non-GBK bytes, cascading into pipe buffer fills, event loop
stalls, and TUI freezes (issues #47939, #53428, #57238).

Scope narrowed per triage feedback: the other 5 sites should land via #55339.

Refs #53428 (together with #55339).

hermes_cli/onepassword_secrets_cli.py

@@ -514,7 +514,8 @@ def _op_whoami(
         env["OP_SERVICE_ACCOUNT_TOKEN"] = token_value
     try:
         res = subprocess.run(
-            cmd, env=env, capture_output=True, text=True, timeout=10
+            cmd, env=env, capture_output=True, text=True,
+            encoding="utf-8", errors="replace", timeout=10
         )
     except (OSError, subprocess.TimeoutExpired):
         return None