[+] Docs

README_DEVELOPER.md

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+## Development server
+
+### Requirements
+- Bun
+- Docker
+
+### 1. Environment setup
+1. Create your `.env` file by renaming `.env.example` to `.env`
+2. Add the following variable:
+   OPENROUTER_API_KEY=your_key_here
+   (Request the key from the repository owner)
+
+### 2. Start the database
+Run in the project root:
+docker compose up
+
+### 3. Install dependencies
+Install Bun:
+https://bun.com/get
+
+Then install project dependencies:
+bun install
+
+### 4. Start development server
+bun run dev