refactor: extract escapeRegex and validateTagSlugs server utils

Deduplicate tag validation and regex escaping into shared auto-imported
utils. Add tag validation to wiki patch/batch-tag routes. Remove
duplicate tags field from event schema.

server/utils/escapeRegex.js

@@ -0,0 +1,3 @@
+export function escapeRegex(str) {
+  return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
+}