feat: initialize ingest-api with Koa and telemetry handling

- Create ingest-api with Koa framework for handling device telemetry.
- Implement telemetry ingestion with MongoDB, Redis, and PostgreSQL.
- Add API endpoints for telemetry and health checks.
- Set up testing with Vitest for unit and end-to-end tests.
- Configure Prettier and ESLint for code formatting and linting.
- Create Docker Compose setup for PostgreSQL, MongoDB, and Redis services.
- Establish contracts package for shared Zod schemas and TypeScript types.
- Implement React frontend with device status and greeting functionalities.
- Add VS Code setup documentation for onboarding developers.

packages/contracts/src/presence.ts

@@ -0,0 +1,4 @@
+/** Redis TTL and Postgres "online" window for the demo. */
+export const PRESENCE_TTL_SECONDS = 15;
+
+export const DEMO_DEVICE_ID = 'dev-1';