fix: use Node 22 for web — matches package.json engine requirement

- Add root nixpacks.toml: npm ci --legacy-peer-deps (ignore scripts),
  then prisma generate, then build:production
- NPM_CONFIG_IGNORE_SCRIPTS prevents postinstall during npm ci

Made-with: Cursor

.node-version

@@ -1 +1 @@
-20
+22

nixpacks.toml

@@ -0,0 +1,7 @@
+providers = ["node"]
+
+[phases.install]
+cmds = ["NPM_CONFIG_IGNORE_SCRIPTS=true npm ci --legacy-peer-deps"]
+
+[phases.build]
+cmds = ["npx prisma generate && npm run build:production"]