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/README.md

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+# contracts
+
+Zod schemas and TypeScript types shared by ingest-api, crud-api, and web.
+
+This package depends on **zod only**. Do not add Koa, Express, Mongo, or trest here — the frontend workspace should stay installable with `yarn workspaces focus web`.

packages/contracts/package.json

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+{
+  "name": "contracts",
+  "private": true,
+  "version": "0.0.1",
+  "type": "module",
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "dependencies": {
+    "zod": "^3"
+  }
+}

packages/contracts/src/device-status.ts

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+import { z } from 'zod';
+
+export const deviceStatusSourceSchema = z.enum(['postgres', 'redis', 'missing']);
+
+export const deviceStatusSchema = z.object({
+  deviceId: z.string().min(1),
+  lastSeen: z.string().datetime().nullable(),
+  payload: z.record(z.unknown()),
+  online: z.boolean(),
+  source: deviceStatusSourceSchema,
+  ageMs: z.number().int().nonnegative().nullable(),
+});
+
+export const deviceStatusPairSchema = z.object({
+  postgres: deviceStatusSchema,
+  redis: deviceStatusSchema,
+});
+
+export type DeviceStatus = z.infer<typeof deviceStatusSchema>;
+export type DeviceStatusPair = z.infer<typeof deviceStatusPairSchema>;

packages/contracts/src/greeting.ts

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+import { z } from 'zod';
+
+export const greetingQuerySchema = z.object({
+  name: z.string().min(1),
+});
+
+export const greetingOutputSchema = z.object({
+  message: z.string(),
+});
+
+export type GreetingQuery = z.infer<typeof greetingQuerySchema>;
+export type GreetingOutput = z.infer<typeof greetingOutputSchema>;

packages/contracts/src/index.ts

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+export * from './device-status.js';
+export * from './greeting.js';
+export * from './presence.js';
+export * from './telemetry.js';

packages/contracts/src/presence.ts

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

packages/contracts/src/telemetry.ts

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+import { z } from 'zod';
+
+export const telemetryPayloadSchema = z.record(z.unknown());
+
+export const telemetryIngestSchema = z.object({
+  deviceId: z.string().min(1),
+  sentAt: z.string().datetime(),
+  payload: telemetryPayloadSchema,
+});
+
+export type TelemetryIngest = z.infer<typeof telemetryIngestSchema>;