feat: native shopping list — decouple from Bring! (#105)

- New shopping_list SQLite table (migration in migrateDB)
- shoppingGetList/Add/Remove — delegates to Bring! or internal DB
  based on SHOPPING_MODE env var (default: internal)
- isShoppingBringMode() guard: requires mode=bring + BRING credentials
- bringQuickSyncProduct updated to support both modes
- All bring_* JS calls replaced with shopping_* (bring_migrate_names kept)
- New settings tab 'Lista spesa' (tab-bring) with:
  - Enable/disable shopping list toggle
  - Provider radio: internal vs Bring!
  - Bring! sub-section (shown only when mode=bring)
  - AI smart suggestions toggle
  - Forecast toggle
  - Auto-add threshold (qty slider)
  - Price estimation section
- _applyShoppingSettingsUI, onShoppingEnabledChange, onShoppingModeChange
- SHOPPING_* env vars documented in .env.example
- cron_smart_shopping respects SHOPPING_MODE and SHOPPING_SMART_SUGGESTIONS
- Translations: 12 new keys in all 5 languages (it/en/de/fr/es)
- DB busy_timeout=5000ms + WAL pragma in getDB() (fixes #95)

translations/de.json

@@ -849,7 +849,22 @@
       "currency_title": "Währung",
       "currency_hint": "Die Währung, die für alle Kosten und Preise in der App verwendet wird."
     },
-    "tab_general": "Allgemein"
+    "tab_general": "Allgemein",
+    "shopping": {
+      "tab": "Einkaufsliste",
+      "title": "Einkaufsliste",
+      "hint": "Konfiguriere die integrierte Einkaufsliste oder verbinde Bring!.",
+      "enable_label": "Einkaufsliste aktivieren",
+      "mode_label": "Anbieter",
+      "mode_internal": "Intern (ohne Bring!)",
+      "mode_bring": "Bring! (externe App)",
+      "bring_section_title": "Bring!-Konfiguration",
+      "ai_section_title": "KI-Unterstützung",
+      "smart_suggestions_label": "KI-Vorschläge",
+      "forecast_label": "Prognose für bald leere Produkte",
+      "auto_add_label": "Automatisch hinzufügen wenn",
+      "auto_add_suffix": "im Lager verbleibend (0 = nur wenn leer)"
+    }
   },
   "expiry": {
     "today": "HEUTE",