release: v1.7.23

- README: update feature callout to v1.7.23, add DB maintenance section,
  update dark mode description (time-based auto), add vacuum-sealed expiry
  paragraph, add new .env params (retention, vacuum, Gemini costs)
- CHANGELOG: add v1.7.23 entry (Generali tab, DB cleanup, vacuum expiry,
  AI tracking, time-based theme, ZeroWaste/screensaver save fix)
- manifest.json: version 1.7.22 → 1.7.23
- index.html: version label and preloader updated to v1.7.23; asset v=20260518c

index.html

@@ -64,7 +64,7 @@
         <div id="preloader-warnings" class="preloader-warnings" style="display:none"></div>
         <div id="preloader-error-msg" class="preloader-error-msg" style="display:none"></div>
         <button id="preloader-retry-btn" class="preloader-retry-btn" style="display:none" onclick="_startupRetry()">🔄 <span data-i18n="startup.retry">Riprova</span></button>
-        <span class="app-preloader-version" id="preloader-version">v1.7.22</span>
+        <span class="app-preloader-version" id="preloader-version">v1.7.23</span>
     </div>
 </div>
 
@@ -77,7 +77,7 @@
         <!-- Title — left-aligned; grows to fill space -->
         <div class="header-title-wrap">
             <h1 class="header-title" onclick="showPage('dashboard')">
-                <img src="assets/img/logo/logo_icon.png" alt="" class="header-logo-icon" aria-hidden="true" /><span data-i18n="nav.title">EverShelf</span><span class="header-version">v1.7.22</span>
+                <img src="assets/img/logo/logo_icon.png" alt="" class="header-logo-icon" aria-hidden="true" /><span data-i18n="nav.title">EverShelf</span><span class="header-version">v1.7.23</span>
             </h1>
             <!-- Update badge — shown alongside title, never replaces it -->
             <span class="header-update-badge" id="header-update-badge" style="display:none"></span>
@@ -1652,6 +1652,6 @@
     </div>
 </div>
 
-<script src="assets/js/app.js?v=20260518b"></script>
+<script src="assets/js/app.js?v=20260518c"></script>
 </body>
 </html>