Replace the page-reload IPC handling in the theme-changed listener with an
in-place toggle of the preloaded <link id="theme-*"> tags. The helper scans
for a matching link first and only mutates disabled states when one exists,
so an unknown id (or main-process miss) short-circuits and preserves the
currently active theme. body.className is always set to the requested id so
legacy selectors keep matching.
Add tests/theme-renderer-apply.test.js with three cases covering: switching
to a fresh theme, idempotent re-switch, and the unknown-id short-circuit.
The test's local helper mirrors the renderer implementation so future drift
is caught at test time.
Amit Haridas
