fix: version string was 021.4, not 0.21.4

The release prompt was answered with a missing dot and the script propagated
it verbatim into both constants, so the shipped exe reported "021.4".

That is not cosmetic: versionLess splits on dots, so "021.4" parses as [21,4]
and compares GREATER than "0.21.5" — a client on that build would be told it
is up to date forever and never offered another update. It also broke the
What's new dialog on a fresh install, where the changelog entry ("0.21.4") is
matched against appVersion by string equality.

Same code as the release otherwise; only the version string changes.

telemetry.go

@@ -21,7 +21,7 @@ import (
 
 const (
 	// appVersion is stamped on every heartbeat (and could feed the About box).
-	appVersion = "021.4"
+	appVersion = "0.21.4"
 
 	// posthogHost is the PostHog ingestion endpoint. EU cloud by default; change
 	// to https://us.i.posthog.com for a US project.