feat: Info tab enriched — retroactive AI estimate, annual totals, inventory & activity stats

api/index.php:
- gemini_usage: retroactive AI call estimate from cache files (price/shelf/category)
  with per-entry token estimates (price ~475tok, shelf ~580tok, category ~230tok)
- yearly totals: sum tracked months + retro estimate for full 2026 view
- DB activity stats: products, inventory, transactions, expired, expiring_soon
- cache stats: price (255), shelf (30), category (7), foodfacts (10)
- system info: last backup timestamp+size, Bring! token expiry
- new constants: SHELF_CACHE_PATH, FOODFACTS_CACHE_PATH, BRING_TOKEN_PATH

assets/js/app.js:
- _renderInfoTab(): full rewrite — 4 cards (AI, Inventory, Activity, System)
- month displayed as localized name via Intl.DateTimeFormat (es. 'maggio 2026')
- tracked section shown when calls > 0; retro estimate always shown if gap exists
- year section: tracked + retro combined total
- pill() helper for consistent stat display

index.html: 4 cards with ids info-ai-content, info-inv-content, info-act-content, info-system-content

translations: updated settings.info.* keys in it/en/de (overview subtitle, retro labels, inv/act/system keys)

translations/it.json

@@ -771,14 +771,37 @@
       "est_cost": "Costo stimato",
       "input_tok": "Token input",
       "output_tok": "Token output",
-      "ai_calls": "Chiamate AI",
+      "ai_calls": "Chiamate",
       "by_action": "Dettaglio per funzione",
       "by_model": "Dettaglio per modello",
-      "pricing_note": "Prezzi di riferimento: gemini-2.5-flash $0.15/1M input, $0.60/1M output.",
+      "pricing_note": "Prezzi di riferimento Gemini: 2.5-flash $0.15/M in · $0.60/M out — 2.0-flash $0.10/M in · $0.40/M out.",
       "system_title": "Sistema",
-      "db_size": "Dimensione database",
-      "log_size": "Dimensione log",
-      "log_level": "Livello di log"
+      "db_size": "Database",
+      "log_size": "Log",
+      "log_level": "Livello log",
+      "ai_overview": "Prospetto utilizzo AI, inventario e stato del sistema",
+      "tracked_section": "Tracciato (da inizio monitoraggio)",
+      "retro_section": "Stima retroattiva — {month}",
+      "retro_note": "Stima basata sulle voci presenti nei file di cache AI, generati prima dell'attivazione del monitoraggio.",
+      "year_section": "Anno {year} — totale stimato",
+      "calls_unit": "call",
+      "inv_title": "Inventario",
+      "inv_active": "Attivi",
+      "inv_products": "Prodotti totali",
+      "inv_expiring": "In scadenza (7gg)",
+      "inv_expired": "Scaduti",
+      "inv_finished": "Finiti",
+      "act_title": "Attività del mese",
+      "act_tx_month": "Movimenti",
+      "act_restock": "Acquisti",
+      "act_use": "Consumi",
+      "act_new_products": "Nuovi prodotti",
+      "act_tx_year": "Movimenti anno",
+      "price_cache": "Cache prezzi",
+      "cache_entries": "prodotti",
+      "last_backup": "Ultimo backup",
+      "bring_days": "token scade tra {n} giorni",
+      "bring_expired": "token scaduto"
     }
   },
   "expiry": {