fix: pin logrotate config mode in image and fail loud on bad permissions

COPY --chmod makes /etc/logrotate.d/mail 0644 regardless of build context
file modes (Windows tar sync). logrotate-loop preflight exits non-zero when
logrotate would ignore the config. E2e covers mode, forced rotation, and a
group-writable context build.

Co-Authored-By: Composer 2.5 <noreply@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

test/e2e/main_test.go

@@ -105,6 +105,12 @@ func TestE2E(t *testing.T) {
 		if err := checkSupervisorProcesses(h); err != nil {
 			t.Fatal(err)
 		}
+		if err := checkLogrotateConfigMode(h); err != nil {
+			t.Fatal(err)
+		}
+		if err := checkLogrotateRotation(h); err != nil {
+			t.Fatal(err)
+		}
 		if err := waitForPanelReady(); err != nil {
 			t.Fatal(err)
 		}