fix(deps): unbreak [all] install — drop mistralai while PyPI quarantined (#24205)

The `mistralai` PyPI package was quarantined on 2026-05-12 after a
malicious 2.4.6 release. Every fresh resolve (AUR makepkg, Docker build,
CI run, install.sh first-run) currently fails on
`mistralai>=2.3.0,<3` because PyPI returns zero candidates.

Existing users running `hermes update` mostly didn't notice — `hermes
update` falls back from `.[all]` to per-extra retries and silently
skips mistral with a warning that scrolls past. But fresh installs
hard-fail or lose every other extra.

Changes:
- pyproject.toml: drop `hermes-agent[mistral]` from `[all]` and
  `[termux-all]`. The `mistral` extra itself is preserved so users
  can opt back in once PyPI un-quarantines.
- hermes_cli/tools_config.py: hide Mistral Voxtral TTS from the
  `hermes tools` provider picker until restored.
- hermes_cli/web_server.py: drop "mistral" from dashboard STT options.
- tools/transcription_tools.py: explicit `provider: mistral` returns
  "none" with a clear status message; auto-detect skips mistral.
- tools/tts_tool.py: dispatcher returns a clear "temporarily disabled"
  error before any SDK import attempt (avoids cached-stale-package
  surprises).
- tests/tools/: update three test files to assert the new disabled
  behavior. Each test docstring records why and points at the rollback
  trigger (PyPI un-quarantines mistralai).

Restore plan: revert this commit once the package is available on PyPI
again. The behavior change is intentional and documented in code
comments + test docstrings to make the rollback trivial.

Validation:
- scripts/run_tests.sh tests/tools/ -k 'mistral or stt or tts' →
  425/425 passing.

Refs: https://pypi.org/simple/mistralai/ (currently
"pypi:project-status: quarantined").

tools/tts_tool.py

@@ -1662,16 +1662,21 @@ def text_to_speech_tool(
             _generate_xai_tts(text, file_str, tts_config)
 
         elif provider == "mistral":
-            try:
-                _import_mistral_client()
-            except ImportError:
-                return json.dumps({
-                    "success": False,
-                    "error": "Mistral provider selected but 'mistralai' package not installed. "
-                             "Run: pip install 'hermes-agent[mistral]'"
-                }, ensure_ascii=False)
-            logger.info("Generating speech with Mistral Voxtral TTS...")
-            _generate_mistral_tts(text, file_str, tts_config)
+            # `mistralai` PyPI package was quarantined on 2026-05-12 after a
+            # malicious 2.4.6 release. Surface a clear status message instead
+            # of attempting an import that would either fail or pull a stale
+            # cached package.
+            return json.dumps({
+                "success": False,
+                "error": (
+                    "Mistral Voxtral TTS is temporarily disabled. The "
+                    "`mistralai` PyPI package was quarantined on 2026-05-12 "
+                    "after a malicious 2.4.6 release. Switch tts.provider in "
+                    "config.yaml to 'edge', 'elevenlabs', 'openai', 'minimax', "
+                    "'gemini', 'xai', 'neutts', or 'kittentts'. Mistral "
+                    "support will return once PyPI un-quarantines the package."
+                ),
+            }, ensure_ascii=False)
 
         elif provider == "gemini":
             logger.info("Generating speech with Google Gemini TTS...")