chore: disable minification of dist bundles

[John-David Dalton (jdalton)]

Summary

• Removes the terser minification plugin from the rollup config
• The dist bundles are now readable and easier to review in PRs

This makes it nicer for everyone to see exactly what's in the bundled output when reviewing changes. The dist files are a bit bigger now but that's totally fine since GitHub Actions downloads them once and they're not served to browsers or anything like that.

Test plan

• Verify npm run build still produces working dist/main.js and dist/post.js
• Confirm the action runs correctly in a workflow