fix(i18n): add missing menu translations and fix admin language resolution

Two issues caused the admin sidebar to show a mix of French and English:

1. Only 3 of 14 modules had "menu" translations in their locale files.
   When a key was missing, _translate_label() fell back to English Title
   Case from the key name — mixing with French from modules that had
   translations. Added menu sections to all 4 languages (en, fr, de, lb)
   across 13 modules.

2. The language middleware hardcoded admin to "en" ignoring user preference,
   while the menu API fell back to DEFAULT_LANGUAGE ("fr") when
   preferred_language was NULL. Fixed middleware to respect user's
   preferred_language and menu API to use middleware-resolved language
   as fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/core/routes/api/admin_menu_config.py

@@ -18,7 +18,7 @@ Menu rendering endpoints require authenticated admin/store access.
 import logging
 from typing import Any
 
-from fastapi import APIRouter, Depends, Path, Query
+from fastapi import APIRouter, Depends, Path, Query, Request
 from pydantic import BaseModel, Field
 from sqlalchemy.orm import Session
 
@@ -180,6 +180,7 @@ def _build_menu_config_response(
 
 @router.get("/platforms/{platform_id}", response_model=MenuConfigResponse)
 async def get_platform_menu_config(
+    request: Request,
     platform_id: int = Path(..., description="Platform ID"),
     frontend_type: FrontendType = Query(
         FrontendType.ADMIN, description="Frontend type (admin or store)"
@@ -203,8 +204,8 @@ async def get_platform_menu_config(
         f"for platform {platform.code} ({frontend_type.value})"
     )
 
-    # Use user's preferred language, falling back to default
-    language = current_user.preferred_language or DEFAULT_LANGUAGE
+    # Use user's preferred language, falling back to middleware-resolved language
+    language = current_user.preferred_language or getattr(request.state, "language", "en")
 
     return _build_menu_config_response(
         items, frontend_type, language=language, platform_id=platform_id
@@ -317,6 +318,7 @@ async def reset_platform_menu_config(
 
 @router.get("/user", response_model=MenuConfigResponse)
 async def get_user_menu_config(
+    request: Request,
     db: Session = Depends(get_db),
     current_user: UserContext = Depends(get_current_super_admin),
 ):
@@ -331,8 +333,8 @@ async def get_user_menu_config(
         f"[MENU_CONFIG] Super admin {current_user.email} fetched their personal menu config"
     )
 
-    # Use user's preferred language, falling back to default
-    language = current_user.preferred_language or DEFAULT_LANGUAGE
+    # Use user's preferred language, falling back to middleware-resolved language
+    language = current_user.preferred_language or getattr(request.state, "language", "en")
 
     return _build_menu_config_response(
         items, FrontendType.ADMIN, language=language, user_id=current_user.id
@@ -442,6 +444,7 @@ async def show_all_platform_menu_config(
 
 @router.get("/render/admin", response_model=RenderedMenuResponse)
 async def get_rendered_admin_menu(
+    request: Request,
     db: Session = Depends(get_db),
     current_user: UserContext = Depends(get_current_admin_from_cookie_or_header),
 ):
@@ -482,8 +485,8 @@ async def get_rendered_admin_menu(
             is_super_admin=False,
         )
 
-    # Use user's preferred language, falling back to default
-    language = current_user.preferred_language or DEFAULT_LANGUAGE
+    # Use user's preferred language, falling back to middleware-resolved language
+    language = current_user.preferred_language or getattr(request.state, "language", "en")
 
     # Translate section and item labels
     sections = []