docs(voice): use uv pip install faster-whisper in STT install hints (#29800)

* docs(voice): use `uv pip install faster-whisper` in STT install hints

Three runtime messages told users to `pip install faster-whisper`
(reported in #29782 for the gateway STT failure message under
Telegram-in-Docker, where the user hit `bash: pip: command not
found`). The Hermes Docker image is built on `ghcr.io/astral-sh/uv`
with a uv-managed venv that doesn't ship `pip` on PATH; users on
modern `uv tool install` / `uv venv` installs see the same problem.

The canonical install command in this repo is `uv pip install`
(see `tools/lazy_deps.py:509` `feature_install_command()`), which
works in Docker (uv image), in `uv tool install` venvs, and in
pip-based venvs that already have uv on PATH.

Changed three locations to match:

- `gateway/run.py` — Telegram/Discord/Slack/WhatsApp/etc. voice
  reply when no STT provider is configured. Suggests
  `uv pip install faster-whisper` and notes that
  `pip install faster-whisper` also works if `pip` is on PATH.
- `tools/voice_mode.py` — `/voice` status line for missing STT.
- `cli.py` — Voice-mode startup error, "Option 1".

No behavior change beyond the user-facing text. No production
code path was touched.

* docs(voice): add pip fallback to cli + voice_mode STT hints

Copilot flagged that cli.py and tools/voice_mode.py recommend
`uv pip install faster-whisper` without a fallback for environments
where uv isn't on PATH. The gateway/run.py message already lists
`pip install faster-whisper` as an alternative; this commit aligns
the two remaining call sites to match.

Addresses inline Copilot review on #29800.

---------

Co-authored-by: briandevans <252620095+briandevans@users.noreply.github.com>

tools/voice_mode.py

@@ -1090,7 +1090,8 @@ def check_voice_requirements() -> Dict[str, Any]:
         details_parts.append("STT provider: OK (OpenAI)")
     else:
         details_parts.append(
-            "STT provider: MISSING (pip install faster-whisper, "
+            "STT provider: MISSING (uv pip install faster-whisper — "
+            "`pip install faster-whisper` also works if pip is on PATH, "
             "or set GROQ_API_KEY / VOICE_TOOLS_OPENAI_KEY)"
         )