feat: link each changelog entry to its PR and commit

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/update/update_test.go

@@ -123,3 +123,10 @@ func TestInstallRefusesATamperedArchive(t *testing.T) {
 		t.Error("replaced anyway")
 	}
 }
+
+func TestNotesShowLinksAsText(t *testing.T) {
+	r := Release{Body: "### Added\n\n- Search ([#11](https://git.example.com/pulls/11)) ([65dc2d7](https://git.example.com/commit/65dc2d7abc))\n\n## Install\n\ncurl …"}
+	if got, want := r.Notes(), "### Added\n\n- Search (#11) (65dc2d7)"; got != want {
+		t.Errorf("notes %q, want %q", got, want)
+	}
+}