feat: Help - What's new button to reopen the changelog anytime

Adds GetChangelog (all entries up to the running version, no seen-marker change)
and a Help menu 'What's new' item that reopens the changelog dialog on demand.

changelog.go

@@ -31,6 +31,20 @@ func loadChangelog() []ChangelogEntry {
 	return out
 }
 
+// GetChangelog returns every changelog entry up to the running version (newest
+// first), without touching the "seen" marker — for a "What's new" button that
+// reopens the notes on demand.
+func (a *App) GetChangelog() []ChangelogEntry {
+	out := []ChangelogEntry{}
+	for _, e := range loadChangelog() {
+		if strings.TrimSpace(e.Version) == "" || versionLess(appVersion, e.Version) {
+			continue
+		}
+		out = append(out, e)
+	}
+	return out
+}
+
 // GetWhatsNew returns the changelog entries the operator hasn't seen yet — the
 // notes for every version newer than the last one they ran, up to the current
 // build — and records the current version as seen so it pops exactly once per