fix: harden webhook reliability, fix bugs, add test suite

- Statuspage webhook always returns 200 to prevent subscriber removal
- Fix parseKvKey returning string chatId instead of number
- Queue consumer retries on Telegram 5xx instead of acking (prevents message loss)
- Fix observability top-level enabled flag (false → true)
- Add defensive null checks for webhook payload body
- Cache Bot instance per isolate to avoid middleware rebuild per request
- Add vitest + @cloudflare/vitest-pool-workers with 31 tests
- Document DLQ and KV sharding as declined features

package.json

@@ -6,7 +6,9 @@
   "type": "module",
   "scripts": {
     "dev": "wrangler dev",
-    "deploy": "wrangler deploy"
+    "deploy": "wrangler deploy",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "repository": {
     "type": "git",
@@ -24,6 +26,8 @@
     "hono": "^4.12.12"
   },
   "devDependencies": {
+    "@cloudflare/vitest-pool-workers": "^0.14.2",
+    "vitest": "^4.1.3",
     "wrangler": "^4.81.0"
   }
 }