first commit of refactor

backend/ENV_TEMPLATE.md

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+# Environment Variables Template
+
+Copy this to `.env` in the backend directory and fill in your values.
+
+```bash
+# Server Configuration
+PORT=3001
+NODE_ENV=development
+
+# Database Configuration
+DATABASE_URL=postgresql://user:password@localhost:5432/koin_ping
+
+# Ethereum JSON-RPC Endpoint
+# Examples:
+#   - Infura: https://mainnet.infura.io/v3/YOUR-PROJECT-ID
+#   - Alchemy: https://eth-mainnet.g.alchemy.com/v2/YOUR-API-KEY
+#   - Local node: http://localhost:8545
+ETH_RPC_URL=https://mainnet.infura.io/v3/YOUR-PROJECT-ID
+
+# Polling interval in milliseconds
+# Default: 60000 (1 minute)
+POLL_INTERVAL_MS=60000
+
+# Firebase Configuration (for authentication)
+# Get this from Firebase Console > Project Settings > Project ID
+FIREBASE_PROJECT_ID=koin-ping
+```
+
+## Quick Setup
+
+```bash
+cd backend
+cp ENV_TEMPLATE.md .env
+# Edit .env with your actual values
+```
+
+## Firebase Setup
+
+For Firebase Admin SDK to work, you need to set up Application Default Credentials:
+
+**Option 1: Use Firebase Project ID (easiest for development)**
+- Just set `FIREBASE_PROJECT_ID` in .env
+- Firebase Admin will use Application Default Credentials
+
+**Option 2: Use Service Account Key (production)**
+1. Go to Firebase Console > Project Settings > Service Accounts
+2. Click "Generate new private key"
+3. Download the JSON file
+4. Either:
+   - Set `GOOGLE_APPLICATION_CREDENTIALS=/path/to/serviceAccountKey.json` in .env
+   - Or keep it in backend/ and add to .gitignore