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

translations/en.json

@@ -1203,15 +1203,33 @@
     "btn_title": "Export"
   },
   "startup": {
-    "check_php": "PHP",
-    "check_exts": "PHP extensions",
+    "connecting": "Connecting to server...",
+    "check_php_memory": "PHP memory",
+    "check_php_timeout": "PHP timeout",
+    "check_php_upload": "PHP upload",
     "check_data_dir": "Data directory",
-    "check_db": "Database",
-    "check_env": "Configuration (.env)",
+    "check_rate_limits": "Rate limits dir",
+    "check_backups": "Backup dir",
+    "check_write_test": "Disk write test",
+    "check_disk_space": "Disk space",
+    "check_db_connect": "Database connection",
+    "check_db_tables": "Database tables",
+    "check_db_integrity": "Database integrity",
+    "check_db_wal": "WAL mode",
+    "check_db_size": "Database size",
+    "check_db_rows": "Inventory data",
+    "check_env": ".env file",
     "check_gemini": "Gemini AI key",
-    "check_bring": "Bring! token",
+    "check_bring_creds": "Bring! credentials",
+    "check_bring_token": "Bring! token",
+    "check_curl_ssl": "cURL SSL",
+    "check_internet": "Internet connection",
+    "fresh_install": "fresh install",
+    "warnings_found": "warnings found",
+    "all_ok": "System OK",
+    "critical_error_short": "Critical error",
     "critical_error": "Critical error: the app cannot start. Check your server logs.",
-    "error_network": "Cannot reach the server. Check your connection.",
+    "error_network": "Cannot reach the server. Check your network connection.",
     "retry": "Retry"
   }
 }