chore: add .env.example template files

Add environment variable templates for:
- Root .env.example (all services)
- backend/.env.example (API configuration)
- frontend/.env.local.example (client config)

Copy to .env and fill in your secrets before running.

backend/.env.example

@@ -1,5 +1,8 @@
+# Backend Environment Variables
+# Copy to .env and fill in your values
+
 # Database
-DATABASE_URL="postgresql://coop:coop_password@localhost:5432/coop_credits?schema=public"
+DATABASE_URL="postgresql://coop:password@localhost:5432/coop_credits?schema=public"
 
 # Server
 PORT=3001
@@ -7,32 +10,32 @@ NODE_ENV=development
 API_URL=http://localhost:3001
 FRONTEND_URL=http://localhost:3000
 
-# JWT
-JWT_SECRET=your-super-secret-jwt-key-change-this-in-production
-JWT_EXPIRES_IN=7d
+# JWT (generate: openssl rand -hex 32)
+JWT_SECRET=""
 
 # Plex OAuth
-PLEX_CLIENT_ID=your-plex-client-id
-PLEX_CLIENT_SECRET=your-plex-client-secret
+PLEX_CLIENT_ID=""
+PLEX_CLIENT_SECRET=""
 PLEX_REDIRECT_URI=http://localhost:3000/auth/callback
 
 # Tautulli
-TAUTULLI_URL=http://localhost:8181
-TAUTULLI_API_KEY=your-tautulli-api-key
-TAUTULLI_WEBHOOK_SECRET=your-webhook-secret
+TAUTULLI_URL=http://172.20.1.255:8181
+TAUTULLI_API_KEY=""
+TAUTULLI_WEBHOOK_SECRET=""
 
 # Overseer
-OVERSEER_URL=http://localhost:5055
-OVERSEER_API_KEY=your-overseer-api-key
+OVERSEER_URL=http://172.20.1.225:5055
+OVERSEER_API_KEY=""
 
 # Solana
 SOLANA_RPC_URL=https://api.devnet.solana.com
 SOLANA_PROGRAM_ID=CoopCredits111111111111111111111111111111111
-SOLANA_MINT_AUTHORITY_KEYPAIR=your-base58-encoded-keypair-for-minting
+SOLANA_MINT_AUTHORITY_KEYPAIR=""
 SOLANA_TOKEN_DECIMALS=6
 
-# Redis (optional - for caching and pub/sub)
-REDIS_URL=redis://localhost:6379
+# Security
+ENCRYPTION_KEY=""
+TRUST_PROXY=false
 
-# Encryption (for wallet private keys)
-ENCRYPTION_KEY=your-32-char-encryption-key!!
+# Redis (optional)
+REDIS_URL=redis://localhost:6379