feat: progress bar startup check with 29 diagnostics (v1.7.21)

- Replace banner checklist with real-time progress bar + per-check label
  Bar fills smoothly (0→100%) as each check runs; label shows current check.
  On success: bar stays green briefly then fades. On warnings: amber badges
  shown for 2.2s. On critical error: bar turns red + error block + Retry.
- Extend health_check to 29 comprehensive checks:
  PHP 8.0+ version, 4 critical extensions (pdo_sqlite/curl/json/mbstring),
  4 optional extensions (openssl/fileinfo/zip/intl), PHP memory/timeout/upload,
  data/ writable, rate_limits/ dir, backups/ dir, actual file-write test,
  free disk space, SQLite connect, required tables, PRAGMA quick_check integrity,
  WAL mode, DB file size, inventory row count, .env file, Gemini AI key,
  Bring! credentials + token, cURL SSL version, internet reachability (Gemini API)
- Fresh-install detection: if dispensa.db not found + data/ writable → OK (auto-create)
- Translations: startup.* expanded to 28 keys in IT, EN, DE, FR, ES
- CSS: new .preloader-progress-wrap, .preloader-bar-track, .preloader-bar,
  .preloader-check-label, .preloader-warn-badge; removed old .preloader-checks
- Version: v1.7.21, assets v=20260520b

index.html

@@ -11,7 +11,7 @@
     <title>EverShelf</title>
     <link rel="manifest" href="manifest.json">
     <link rel="icon" type="image/png" href="assets/img/logo/logo_icon.png">
-    <link rel="stylesheet" href="assets/css/style.css?v=20260520a">
+    <link rel="stylesheet" href="assets/css/style.css?v=20260520b">
     <!-- QuaggaJS for barcode scanning -->
     <script src="https://cdn.jsdelivr.net/npm/@ericblade/quagga2@1.8.4/dist/quagga.min.js"></script>
     <!-- @xenova/transformers: ES-module bootstrap that exposes a lazy category-classifier as window._categoryPipelinePromise -->
@@ -55,10 +55,16 @@
     <div class="app-preloader-inner">
         <img src="assets/img/logo/logo.png" alt="EverShelf" class="app-preloader-logo" />
         <div class="app-preloader-spinner" id="preloader-spinner"></div>
-        <div id="preloader-checks" class="preloader-checks" style="display:none"></div>
+        <div id="preloader-progress-wrap" class="preloader-progress-wrap" style="display:none">
+            <div class="preloader-bar-track">
+                <div id="preloader-bar" class="preloader-bar"></div>
+            </div>
+            <div id="preloader-check-label" class="preloader-check-label">&nbsp;</div>
+        </div>
+        <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">v1.7.20</span>
+        <span class="app-preloader-version" id="preloader-version">v1.7.21</span>
     </div>
 </div>
 
@@ -71,7 +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">v1.7.20</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">v1.7.21</span>
             </h1>
             <!-- Update badge — shown alongside title, never replaces it -->
             <span class="header-update-badge" id="header-update-badge" style="display:none"></span>
@@ -1607,6 +1613,6 @@
     </div>
 </div>
 
-<script src="assets/js/app.js?v=20260520a"></script>
+<script src="assets/js/app.js?v=20260520b"></script>
 </body>
 </html>