fix: wire STT lazy-install into transcription_tools.py

The ensure('stt.faster_whisper') lazy-install mechanism was defined in
lazy_deps.py but never called from the STT code path. When
_HAS_FASTER_WHISPER (a module-level constant) evaluated to False at
import time, _get_provider() returned 'none' immediately without
attempting installation. On fresh container builds or venv recreations,
this meant voice message transcription broke silently until someone
manually installed faster-whisper.

Add _try_lazy_install_stt() helper that calls ensure() and
re-checks dynamically via importlib.util.find_spec. Wire it into
all three gates in transcription_tools.py:

- _get_provider() explicit 'local' path (line 221)
- _get_provider() auto-detect path (line 287)
- _transcribe_local() guard (line 405)

This ensures the first voice message after any fresh install triggers
auto-installation instead of failing permanently until a process restart.

tools/transcription_tools.py

@@ -197,6 +197,26 @@ def _normalize_local_command_model(model_name: Optional[str]) -> str:
     return _normalize_local_model(model_name)
 
 
+def _try_lazy_install_stt() -> bool:
+    """Attempt to lazy-install faster-whisper and return True on success.
+
+    The module-level ``_HAS_FASTER_WHISPER`` flag is set at import time and
+    cached. If the package wasn't installed at startup, calling ``ensure()``
+    installs it. This function re-checks dynamically after installation so
+    the provider can use it immediately without a process restart.
+    """
+    try:
+        from tools.lazy_deps import ensure
+        ensure("stt.faster_whisper")
+        # Re-check dynamically after install
+        import importlib.util as _iu
+        if _iu.find_spec("faster_whisper"):
+            return True
+    except Exception:
+        pass
+    return False
+
+
 def _get_provider(stt_config: dict) -> str:
     """Determine which STT provider to use.
 
@@ -218,6 +238,9 @@ def _get_provider(stt_config: dict) -> str:
                 return "local"
             if _has_local_command():
                 return "local_command"
+            # Try lazy-install before giving up
+            if _try_lazy_install_stt():
+                return "local"
             logger.warning(
                 "STT provider 'local' configured but unavailable "
                 "(install faster-whisper or set HERMES_LOCAL_STT_COMMAND)"
@@ -285,6 +308,9 @@ def _get_provider(stt_config: dict) -> str:
         return "local"
     if _has_local_command():
         return "local_command"
+    # Try lazy-install before falling through to cloud providers
+    if _try_lazy_install_stt():
+        return "local"
     if _HAS_OPENAI and get_env_value("GROQ_API_KEY"):
         logger.info("No local STT available, using Groq Whisper API")
         return "groq"
@@ -403,7 +429,8 @@ def _transcribe_local(file_path: str, model_name: str) -> Dict[str, Any]:
     global _local_model, _local_model_name
 
     if not _HAS_FASTER_WHISPER:
-        return {"success": False, "transcript": "", "error": "faster-whisper not installed"}
+        if not _try_lazy_install_stt():
+            return {"success": False, "transcript": "", "error": "faster-whisper not installed"}
 
     try:
         # Lazy-load the model (downloads on first use, ~150 MB for 'base')