Point desktop downloads at 0.3.0; release v5.5.3

The Download block still offered desktop 0.1.0 — the build from before in-app
updates, the voice-note fixes and the verification hardening. Windows, macOS and
Linux now link to 0.3.0.

The version was repeated across three URLs in two different forms: two resolved
through /releases/latest/download/ and one pinned a tag. That is how they drifted
out of date, so it is now one constant.

The tag stays pinned on purpose. Release filenames carry the version, so a
/latest/ link breaks the moment a newer release exists, while a pinned tag keeps
serving a working installer — the safer way to fail if the constant is ever left
behind.

sw.js

@@ -11,7 +11,7 @@ let DYNAMIC_CACHE = 'securebit-pwa-dynamic-v4.7.56';
 // Build stamp — rewritten by scripts/post-build.js on every release so this file's
 // bytes change each deploy. That is what makes the browser detect a new Service Worker,
 // reinstall it, drop stale caches and (via controllerchange) prompt the page to update.
-const SW_BUILD_VERSION = '1785125039593';
+const SW_BUILD_VERSION = '1785141222839';
 
 // Load version from meta.json on install
 async function getAppVersion() {