licence,ci: ship OFL with Plex fonts and guard release dispatch (P5)

IBM Plex WOFF2 files were shipped without the SIL OFL 1.1 text, NOTICE
told modifiers to edit layout.html for a Source URL that lives in
legal.go, and workflow_dispatch took GITHUB_REF_NAME as the version so a
run from main would publish ghcr.io/...:main.

Closes P5 of docs/plans/code-review.md. CHANGELOG updated.

Co-Authored-By: Cursor Grok 4.6 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

internal/legal/license_test.go

@@ -19,3 +19,22 @@ func TestEmbeddedLicenseMatchesRoot(t *testing.T) {
 		t.Fatal("embedded LICENSE is empty")
 	}
 }
+
+// NOTICE used to tell modifiers to edit layout.html for the Source URL. The
+// footer reads legal.SourceURL; a fork that only changed the template would
+// still advertise the upstream repo.
+func TestNoticePointsAtSourceURLConstant(t *testing.T) {
+	notice, err := os.ReadFile(filepath.Join("..", "..", "NOTICE"))
+	if err != nil {
+		t.Fatalf("read NOTICE: %v", err)
+	}
+	if !bytes.Contains(notice, []byte("internal/legal/legal.go")) {
+		t.Error("NOTICE must tell modifiers to update SourceURL in internal/legal/legal.go")
+	}
+	if bytes.Contains(notice, []byte("layout.html")) {
+		t.Error("NOTICE still tells modifiers to edit layout.html for the Source URL")
+	}
+	if !bytes.Contains(notice, []byte("internal/web/view/static/OFL.txt")) {
+		t.Error("NOTICE must point at the OFL text that travels with the Plex fonts")
+	}
+}