The previous approach (source .env && npm run sign:firefox) failed
because npm subshells don't inherit env vars consistently, and
quoted values in .env weren't being stripped.
New approach: sign-firefox.sh reads .env itself, strips quotes,
and passes --api-key/--api-secret directly to web-ext sign.
Also renames web-ext-config.js → web-ext-config.cjs to fix the
deprecation warning, and bumps package.json version to 0.2.0.
https://claude.ai/code/session_01Dvgwe7XMoSxnWXkih8p1Cw
