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

CLAUDE.md

@@ -13,7 +13,10 @@ Telegram bot that forwards [status.claude.com](https://status.claude.com/) (Atla
 - `npx wrangler deploy --dry-run` — Verify build without deploying
 - `node scripts/setup-bot.js` — One-time: register bot commands + set Telegram webhook (interactive prompts)
 
-No test framework configured yet. No linter configured.
+- `npm test` — Run tests (vitest + @cloudflare/vitest-pool-workers, runs in Workers runtime)
+- `npm run test:watch` — Run tests in watch mode
+
+No linter configured.
 
 ## Secrets (set via `wrangler secret put`)