feat: add PostgreSQL config and dependencies

.env.example

@@ -45,3 +45,22 @@ AI_LLM_BASE_URL=https://9router.asepharyana.tech/v1
 AI_LLM_MODEL=free
 AI_ANALYSIS_TIMEOUT_MS=30000
 
+# Database Configuration
+DATABASE_TYPE=sqlite
+# DATABASE_TYPE=postgres
+
+# PostgreSQL Configuration (used when DATABASE_TYPE=postgres)
+# Option 1: Use DATABASE_URL for connection string
+# DATABASE_URL=postgresql://user:password@localhost:5432/discord_bot
+
+# Option 2: Use individual connection parameters
+# POSTGRES_HOST=localhost
+# POSTGRES_PORT=5432
+# POSTGRES_USER=postgres
+# POSTGRES_PASSWORD=your_password_here
+# POSTGRES_DB=discord_bot
+
+# PostgreSQL Connection Pool Configuration
+# POSTGRES_POOL_MIN=2
+# POSTGRES_POOL_MAX=10
+