feat: bootstrap lunch picker miniapp with backend, docs, and branding assets

template/backend/README.md

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+# Lunch Picker Backend
+
+Express API server for Lunch Picker miniapp.
+
+## Modes
+
+- Memory mode: run without MySQL env vars (quick local demo)
+- MySQL mode: set `MYSQL_HOST` (or `MYSQL_URL`) and run with real DB
+
+## 1) Install
+
+```bash
+cd backend
+npm install
+cp .env.example .env
+```
+
+## 2) Start
+
+```bash
+npm start
+```
+
+Server: `http://localhost:4000`
+
+## 3) MySQL setup
+
+1. Create DB (example)
+
+```sql
+create database lunch_picker character set utf8mb4 collate utf8mb4_0900_ai_ci;
+```
+
+2. Apply schema
+
+```bash
+mysql -u root -p lunch_picker < ../docs/db/schema.sql
+```
+
+3. Set `.env` values (`MYSQL_HOST`, `MYSQL_USER`, `MYSQL_PASSWORD`, `MYSQL_DATABASE`)
+
+When MySQL mode starts, seed data is inserted automatically only when `restaurant` table is empty.
+
+## API Endpoints
+
+- `GET /v1/health`
+- `GET /v1/restaurants/nearby`
+- `GET /v1/restaurants/:restaurantId`
+- `GET /v1/restaurants/:restaurantId/reviews`
+- `POST /v1/restaurants/:restaurantId/reviews`
+- `DELETE /v1/reviews/:reviewId`
+- `POST /v1/restaurants/:restaurantId/like`
+- `GET /v1/users/me/reviews`
+
+## Auth Simulation
+
+Set `x-user-id` header to simulate user identity.
+
+Example:
+
+```bash
+curl -H "x-user-id: demo-user-1" "http://localhost:4000/v1/restaurants/nearby?lat=37.501&lng=127.037&radiusMeters=1000&sort=distance"
+```