Migrate to TypeScript with esbuild bundling and Vitest smoke tests

[Valamorde]

Summary

• Converts all Lambda functions from plain JS to TypeScript
• Switches CDK to NodejsFunction (esbuild bundling) — no per-function package.json needed
• Introduces a src/shared/ module for the DDB client singleton, ApiGW factory, key builders, and domain types
• Decomposes the 300-line sendmessage if-chain into a typed dispatch map with one handler file per event type
• Adds Vitest smoke tests (20 tests) covering connect, disconnect, services, and all sendmessage handlers
• Fixes several bugs from the original JS code:
  • objectid declared without const (implicit global) in onconnect
  • for(tokenid in tokens) implicit global in services
  • Batch slice overlap (slice(i, i+21) with i+=20) causing duplicated writes
  • Hardcoded table name "abovevtt" instead of TABLE_NAME env var
  • Dead imports removed (PRIORITY_ABOVE_NORMAL, require('http'))
  • tsconfig.json typo noFalltriganCasesInSwitch corrected

Wire protocol

All HTTP paths, WebSocket eventType values, and JSON response shapes are preserved exactly. The browser extension requires no changes.

Test plan

• pnpm test — all 20 smoke tests pass
• cdk diff — Lambda functions replaced (expected), DynamoDB table unchanged
• End-to-end: WebSocket session with DM + player, scene switch, token move