feat: add contributing guidelines and pull request template; update schema comments and documentation

scripts/i18n-utils.cjs

@@ -2,6 +2,9 @@ const fs = require('fs');
 const path = require('path');
 const vm = require('vm');
 
+// CONTRACT:
+// This list is the script-side locale source of truth. Keep it in sync with
+// webapp/src/lib/i18n.ts whenever adding/removing a locale.
 const localeDir = path.join(__dirname, '..', 'webapp', 'src', 'lib', 'i18n', 'locales');
 
 const localeFiles = [