feat: v1.7.9 — category badges, category search, AI guards

- Category badge on every inventory item (icon + label); 'altro' items
  refined asynchronously via new guess_category Gemini endpoint
  (data/category_ai_cache.json) — no AI call when key not configured
- Category search: inventory search now matches by macro-category key
  and translated label (e.g. 'biscotti' finds all cookie items)
- Brand fast-path in guessCategoryFromName (Oreo, Barilla, Lavazza…)
- Fix: duplicate banner alerts — _bannerLoading guard + _queuedItemIds Set
- Fix: mapToLocalCategory with en:dairies (dairi stem added)
- Fix: mapToLocalCategory no longer blocks on 'altro' — falls back to
  guessCategoryFromName(productName) before returning 'altro'
- Fix: 'Tonno all'olio' was resolving to condimenti — moved tonno\b
  check before olio\b in conserve regex block
- AI guards: _refineCategoryBadgesAsync and fetchAllPrices now check
  _geminiAvailable (JS); getShoppingPrice returns no_api_key (PHP)
  when GEMINI_API_KEY is not set — all AI functions are now explicit

assets/css/style.css

@@ -378,6 +378,51 @@ body {
 
 /* (scan active is defined above in .header-scan-btn:active) */
 
+/* ── Offline / server-unreachable banner ──────────────────────────────── */
+.offline-banner {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 8px;
+    background: #dc2626;
+    color: #fff;
+    padding: 9px 16px;
+    font-size: 0.88rem;
+    font-weight: 600;
+    position: sticky;
+    top: 0;
+    z-index: 950;
+    box-shadow: 0 2px 8px rgba(220,38,38,0.35);
+}
+.offline-banner-icon { font-size: 1rem; line-height: 1; }
+.offline-banner-text { flex: 1; text-align: center; }
+.offline-banner-retry {
+    background: rgba(255,255,255,0.22);
+    border: 1px solid rgba(255,255,255,0.55);
+    color: #fff;
+    border-radius: 6px;
+    padding: 3px 11px;
+    font-size: 0.8rem;
+    font-weight: 600;
+    cursor: pointer;
+    white-space: nowrap;
+    transition: background 0.15s;
+}
+.offline-banner-retry:hover { background: rgba(255,255,255,0.38); }
+
+/* When server is offline, block interactions with the main content */
+body.server-offline .app-content {
+    opacity: 0.4;
+    pointer-events: none;
+    user-select: none;
+    transition: opacity 0.3s;
+}
+body.server-offline .bottom-nav {
+    opacity: 0.4;
+    pointer-events: none;
+    transition: opacity 0.3s;
+}
+
 /* Spesa mode banner */
 .spesa-mode-banner {
     display: flex;
@@ -1098,6 +1143,11 @@ body {
     color: #1d4ed8;
 }
 
+.badge-category {
+    background: #f1f5f9;
+    color: #475569;
+}
+
 .badge-qty {
     background: #d1fae5;
     color: #047857;