Fix the desktop download buttons; release v5.5.4

The buttons still led to a dead GitHub page. 5.5.3 updated one of the two places
these links live — the platforms menu on the connection screen keeps its own
DOWNLOADS table, and it was missed, so it stayed on 0.1.0.

Why it looked like a working link that did nothing: the stale entries used
/releases/latest/download/<file>, and GitHub resolves `latest` by redirecting to
the newest tag. Once 0.3.0 shipped, a link written for 0.1.0 resolved to
/releases/download/v0.3.0/SecureBit.Chat_0.1.0_x64-setup.exe — a file that never
existed under that tag. The browser navigated to GitHub and downloaded nothing.

Both places now build their URLs from a DESKTOP_VERSION constant with the tag
pinned, so the version is written once per file and a link cannot silently
become invalid when a new release goes out.

Adds tests/desktop-download-links.test.mjs, which fails the build if this drifts
again: every source must derive URLs from that constant, /latest/ and hardcoded
versions in filenames are rejected, and each generated URL is fetched to prove
the asset exists. SKIP_NETWORK=1 skips the fetches offline.

index.html

@@ -24,7 +24,7 @@
 
     <!-- PWA Manifest -->
 <link rel="manifest" href="./manifest.json">
-<link rel="icon" type="image/x-icon" href="./logo/favicon.ico?v=1785141222839">
+<link rel="icon" type="image/x-icon" href="./logo/favicon.ico?v=1785142410213">
 
 <!-- PWA Meta Tags -->
 <meta name="mobile-web-app-capable" content="yes">
@@ -90,7 +90,7 @@
     <link rel="apple-touch-startup-image" media="screen and (device-width: 744px) and (device-height: 1133px) and (-webkit-device-pixel-ratio: 2) and (orientation: portrait)" href="./logo/splash/splash_screens/8.3__iPad_Mini_portrait.png">
     
 <!-- Apple Touch Icons -->
-<link rel="apple-touch-icon" href="./logo/icon-180x180.png?v=1785141222839">
+<link rel="apple-touch-icon" href="./logo/icon-180x180.png?v=1785142410213">
 <link rel="apple-touch-icon" sizes="57x57" href="./logo/icon-57x57.png">
 <link rel="apple-touch-icon" sizes="60x60" href="./logo/icon-60x60.png">
 <link rel="apple-touch-icon" sizes="72x72" href="./logo/icon-72x72.png">
@@ -99,7 +99,7 @@
 <link rel="apple-touch-icon" sizes="120x120" href="./logo/icon-120x120.png">
 <link rel="apple-touch-icon" sizes="144x144" href="./logo/icon-144x144.png">
 <link rel="apple-touch-icon" sizes="152x152" href="./logo/icon-152x152.png">
-<link rel="apple-touch-icon" sizes="180x180" href="./logo/icon-180x180.png?v=1785141222839">
+<link rel="apple-touch-icon" sizes="180x180" href="./logo/icon-180x180.png?v=1785142410213">
 
 <!-- Microsoft Tiles -->
 <meta name="msapplication-TileColor" content="#ff6b35">
@@ -183,7 +183,7 @@
     <!-- Render-blocking JS is deferred: classic deferred scripts and module scripts
          both execute in document order after parsing, so React still runs before the
          app modules below, but the parser / first paint is no longer blocked. -->
-    <script defer src="config/ice-servers.js?v=1785141222839"></script>
+    <script defer src="config/ice-servers.js?v=1785142410213"></script>
     <script defer src="libs/react/react.production.min.js"></script>
     <script defer src="libs/react-dom/react-dom.production.min.js"></script>
     <!-- Prism syntax highlighting (vendored, offline). Tokenizes code as TEXT only —
@@ -191,8 +191,8 @@
          Its CSS is loaded async via load-async-css.js (not paint-critical). -->
     <script defer src="libs/prism/prism.js"></script>
     <!-- Critical, paint-defining CSS stays render-blocking (avoids FOUC / layout shift). -->
-    <link rel="stylesheet" href="assets/tailwind.css?v=1785141222839">
-    <link rel="icon" type="image/x-icon" href="/logo/favicon.ico?v=1785141222839">
+    <link rel="stylesheet" href="assets/tailwind.css?v=1785142410213">
+    <link rel="icon" type="image/x-icon" href="/logo/favicon.ico?v=1785142410213">
     <!-- Preload only the fonts needed for first paint. fa-solid covers the bulk of UI
          icons; fa-regular/fa-brands are loaded on demand by their CSS (rarely on the
          first screen). Inter latin 400/700 cover body text and headings/buttons. -->
@@ -200,31 +200,31 @@
     <link rel="preload" href="/assets/fonts/inter/files/inter-latin-400.woff2" as="font" type="font/woff2" crossorigin>
     <link rel="preload" href="/assets/fonts/inter/files/inter-latin-700.woff2" as="font" type="font/woff2" crossorigin>
     <link rel="stylesheet" href="/assets/fonts/inter/inter.css">
-    <link rel="stylesheet" href="src/styles/main.css?v=1785141222839">
-    <link rel="stylesheet" href="src/styles/animations.css?v=1785141222839">
-    <link rel="stylesheet" href="src/styles/components.css?v=1785141222839">
+    <link rel="stylesheet" href="src/styles/main.css?v=1785142410213">
+    <link rel="stylesheet" href="src/styles/animations.css?v=1785142410213">
+    <link rel="stylesheet" href="src/styles/components.css?v=1785142410213">
     <!-- Non-critical CSS (FontAwesome ~102KB, Prism) loaded async — no longer blocks paint. -->
-    <script defer src="src/scripts/load-async-css.js?v=1785141222839"></script>
+    <script defer src="src/scripts/load-async-css.js?v=1785142410213"></script>
     <noscript>
         <link rel="stylesheet" href="/assets/fontawesome/css/all.min.css">
         <link rel="stylesheet" href="libs/prism/prism.css">
     </noscript>
-    <script defer src="src/scripts/fa-check.js?v=1785141222839"></script>
+    <script defer src="src/scripts/fa-check.js?v=1785142410213"></script>
     <!-- Update Manager - система принудительного обновления -->
-    <script defer src="src/utils/updateManager.js?v=1785141222839"></script>
-    <script type="module" src="src/components/UpdateChecker.jsx?v=1785141222839"></script>
-    <script type="module" src="dist/qr-local.js?v=1785141222839"></script>
-    <script type="module" src="src/components/QRScanner.js?v=1785141222839"></script>
+    <script defer src="src/utils/updateManager.js?v=1785142410213"></script>
+    <script type="module" src="src/components/UpdateChecker.jsx?v=1785142410213"></script>
+    <script type="module" src="dist/qr-local.js?v=1785142410213"></script>
+    <script type="module" src="src/components/QRScanner.js?v=1785142410213"></script>
 </head>
 <body>
     <div id="root"></div>
-    <script type="module" src="dist/app-boot.js?v=1785141222839"></script>
-    <script type="module" src="dist/app.js?v=1785141222839"></script>
+    <script type="module" src="dist/app-boot.js?v=1785142410213"></script>
+    <script type="module" src="dist/app.js?v=1785142410213"></script>
 
-<script defer src="src/scripts/pwa-register.js?v=1785141222839"></script>
-<script src="./src/pwa/install-prompt.js?v=1785141222839" type="module"></script>
-<script src="./src/pwa/pwa-manager.js?v=1785141222839" type="module"></script>
-<script defer src="./src/scripts/pwa-offline-test.js?v=1785141222839"></script>
-<link rel="stylesheet" href="./src/styles/pwa.css?v=1785141222839">
+<script defer src="src/scripts/pwa-register.js?v=1785142410213"></script>
+<script src="./src/pwa/install-prompt.js?v=1785142410213" type="module"></script>
+<script src="./src/pwa/pwa-manager.js?v=1785142410213" type="module"></script>
+<script defer src="./src/scripts/pwa-offline-test.js?v=1785142410213"></script>
+<link rel="stylesheet" href="./src/styles/pwa.css?v=1785142410213">
 </body>
 </html>