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out of date, so it is now one constant.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.

meta.json

@@ -1,10 +1,10 @@
 {
-  "version": "1785125039593",
-  "buildVersion": "1785125039593",
-  "appVersion": "5.5.2",
-  "buildTime": "2026-07-27T04:03:59.662Z",
-  "buildId": "1785125039593-b3fcf54",
-  "gitHash": "b3fcf54",
+  "version": "1785141222839",
+  "buildVersion": "1785141222839",
+  "appVersion": "5.5.3",
+  "buildTime": "2026-07-27T08:33:42.891Z",
+  "buildId": "1785141222839-6152a77",
+  "gitHash": "6152a77",
   "generated": true,
-  "generatedAt": "2026-07-27T04:03:59.664Z"
+  "generatedAt": "2026-07-27T08:33:42.893Z"
 }