fix: race condition causing GZIP corruption on restart

[yetval]

Fixes #481

As requested, here's the fix for the restart race condition. Found some more bugs on the way:

• Build now writes to views/dist-new and atomically renames to views/dist on completion, eliminating the window where the server could serve plain HTML with a gzip Content-Encoding
• npm run kill now uses npx pm2 kill; pkill -f "node backend.js" || true instead of pkill node, which was killing the pm2 daemon and leaving nginx with stale connections
• Skip paintSource on vendor scram bundles to fix intermittent esbuild failures on repeated builds