chore: add READMEs for clarity

backend/README.md

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+# minxa.lol – Backend
+
+This is the **FastAPI-based** backend service for [minxa.lol](https://minxa.lol), a modern and lightweight URL shortener.
+
+---
+
+## 🧰 Tech Stack
+
+* **FastAPI** – Async web framework
+* **SQLAlchemy (async)** – Database ORM
+* **PostgreSQL** – Primary data store
+* **Hashids** – Encodes IDs into short strings
+* **Alembic** – Database migrations
+* **Uvicorn** – ASGI server
+
+---
+
+## ⚙️ Environment Setup
+
+### 1. Create a virtual environment
+
+```bash
+python3 -m venv venv
+source venv/bin/activate
+```
+
+### 2. Install dependencies
+
+```bash
+pip install -r requirements.txt
+```
+
+### 3. Create `.env` file
+
+```bash
+cp .env.example .env
+```
+
+Edit the `.env` file to include your local database connection:
+
+```env
+DATABASE_URL=postgresql+asyncpg://user:password@localhost:5432/minxadatabase
+```
+
+---
+
+## 🚀 Running the Backend
+
+### Development Server
+
+```bash
+uvicorn backend.main:app --reload --app-dir ..
+```
+
+### Production Server (via Docker Compose)
+
+From the root of the project:
+
+```bash
+python generate_configs.py
+
+docker compose -f docker-compose.generated.yml up --build -d
+```
+
+---
+
+## 📁 Directory Overview
+
+```
+backend/
+├── db/            # DB engine & session
+├── models/        # SQLAlchemy models
+├── routes/        # FastAPI routers
+├── schemas/       # Pydantic request/response schemas
+├── services/      # Business logic
+├── utils/         # Hashid encoder and other helpers
+├── main.py        # FastAPI entrypoint
+├── config.py      # Environment configuration
+└── requirements.txt
+```
+
+---
+
+## 🧪 Testing (Coming Soon)
+
+Unit and integration tests will be added using **pytest**.