fix(ui): critical translation workflow improvements

- Extracted Translate button to sticky bottom wrapper (always visible)
- Added humanFriendlyError mapper for readable error messages
- Added 'Réessayer' and 'Nouveau fichier' buttons to FAILED state
- Hid GlossarySelector for non-Pro users
- Fixed silent failure: attempted=0 now fails explicitly

routes/translate_routes.py

@@ -1188,14 +1188,23 @@ async def _run_translation_job(
         attempted = stats.get("attempted", 0)
         changed = stats.get("changed", 0)
 
+        if attempted == 0 and file_extension in ('.docx', '.xlsx', '.pptx'):
+            error_msg = (
+                "Aucun texte traduisible détecté dans le document. "
+                "Le fichier est peut-être vide, protégé, ou ne contient que des images."
+            )
+            logger.error(f"Job {job_id}: {error_msg}")
+            tracker.set_error(error_msg)
+            return
+
         if attempted > 0:
             ratio = changed / attempted
             logger.info(f"Job {job_id}: translation stats — {changed}/{attempted} texts changed ({ratio:.0%})")
             if changed == 0:
                 error_msg = (
-                    f"Translation failed: 0 out of {attempted} texts were translated. "
-                    f"The provider ({provider}) may be unavailable or misconfigured. "
-                    f"Check your API keys in admin settings."
+                    f"0 textes sur {attempted} ont été traduits. "
+                    f"Le moteur ({provider}) est peut-être indisponible ou mal configuré. "
+                    f"Vérifiez les clés API dans les paramètres admin."
                 )
                 logger.error(f"Job {job_id}: {error_msg}")
                 tracker.set_error(error_msg)