backfill firmware mirror: 0.9.1 + 0.9.6 uf2s for the panel updater

README.md

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+# firmware mirror
+
+OpenPuck release `.uf2` files, mirrored from the GitHub release assets because
+raw.githubusercontent.com serves files WITH CORS headers while the release-asset CDN does
+not — this is what lets the WebUSB config panel download and flash releases in-browser.
+Maintained automatically by `.github/workflows/release.yml`; do not edit by hand.