Add automated testing flow to reduce manual effort

Integrate a new testkit endpoint and update package.json scripts to enable automated testing via `pnpm test` and `pnpm test:prod`, including a new test case for request body size limits.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 418bf6f8-212b-4bb0-a7a5-8231a061da4e
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 60472e18-59b7-4877-a9a2-16381573ab68
Replit-Helium-Checkpoint-Created: true

scripts/test-local.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+# Runs the Timmy test suite against the local dev server.
+# Usage: pnpm test   (from repo root)
+#        BASE=https://custom-url.replit.app pnpm test
+set -euo pipefail
+BASE="${BASE:-https://${REPLIT_DEV_DOMAIN}}"
+echo "Running tests against: $BASE"
+BASE="$BASE" bash timmy_test.sh