feat: scaffold plug-n-play telegram bot on cloudflare workers

grammY-based bot with a module plugin system loaded from the MODULES env
var. Three command visibility levels (public/protected/private) share a
unified command namespace with conflict detection at registry build.

- 4 initial modules (util, wordle, loldle, misc); util fully implemented,
  others are stubs proving the plugin system end-to-end
- util: /info (chat/thread/sender ids) + /help (pure renderer over the
  registry, HTML parse mode, escapes user-influenced strings)
- KVStore interface with CFKVStore and a per-module prefixing factory;
  getJSON/putJSON convenience helpers; other backends drop in via one file
- Webhook at POST /webhook with secret-token validation via grammY's
  webhookCallback; no admin HTTP surface
- Post-deploy register script (npm run deploy = wrangler deploy && node
  --env-file=.env.deploy scripts/register.js) for setWebhook and
  setMyCommands; --dry-run flag for preview
- 56 vitest unit tests across 7 suites covering registry, db wrapper,
  dispatcher, help renderer, validators, and HTML escaper
- biome for lint + format; phased implementation plan under plans/

src/util/escape-html.js

@@ -0,0 +1,21 @@
+/**
+ * @file escape-html — minimal HTML entity escaper for Telegram HTML parse mode.
+ *
+ * Telegram's HTML parse mode needs only four characters escaped: &, <, >, ".
+ * Keep this as a tiny hand-rolled function — pulling in a library for four
+ * replacements is YAGNI.
+ *
+ * @see https://core.telegram.org/bots/api#html-style
+ */
+
+/**
+ * @param {unknown} s — coerced to string.
+ * @returns {string}
+ */
+export function escapeHtml(s) {
+  return String(s)
+    .replaceAll("&", "&amp;")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;")
+    .replaceAll('"', "&quot;");
+}