Server App Changes

When modifying server apps (webapp, supervisor, etc.) with no package changes, add a .server-changes/ file instead of a changeset:

cat > .server-changes/descriptive-name.md << 'EOF'
---
area: webapp
type: fix
---

Brief description of what changed and why.
EOF

area: webapp | supervisor
type: feature | fix | improvement | breaking
If the PR also touches packages/, just the changeset is sufficient (no .server-changes/ needed).