refactor: Add environment variable support to API server configuration and fix build path

- Add getEnv and getEnvInt helper functions for reading environment variables with defaults
- Update all configuration fields to use environment variables (DB_HOST, REDIS_HOST, API_PORT, etc.)
- Change CI build command from ./cmd/server.go to ./cmd/ directory path

.github/workflows/ci.yml

@@ -65,7 +65,7 @@ jobs:
 
       - name: Build API server
         working-directory: apps/api-server
-        run: go build -o bin/api-server ./cmd/server.go
+        run: go build -o bin/api-server ./cmd/
 
   web-dashboard-test:
     name: Web Dashboard Tests

apps/api-server/internal/config/config.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"os"
+	"strconv"
 	"time"
 )
 
@@ -75,27 +77,43 @@ type AuthConfig struct {
 	JWTSecret string `json:"jwt_secret"`
 }
 
+func getEnv(key, defaultValue string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return defaultValue
+}
+
+func getEnvInt(key string, defaultValue int) int {
+	if value := os.Getenv(key); value != "" {
+		if intVal, err := strconv.Atoi(value); err == nil {
+			return intVal
+		}
+	}
+	return defaultValue
+}
+
 func LoadConfig() *Config {
 	return &Config{
 		Server: ServerConfig{
-			Port:         "8000",
-			MetricsPort:  "9090",
+			Port:         getEnv("API_PORT", "8000"),
+			MetricsPort:  getEnv("METRICS_PORT", "9090"),
 			ReadTimeout:  30 * time.Second,
 			WriteTimeout: 30 * time.Second,
 		},
 		Database: DatabaseConfig{
-			Host:     "localhost",
-			Port:     "5432",
-			Database: "telecom_platform",
-			Username: "postgres",
-			Password: "password",
-			SSLMode:  "disable",
+			Host:     getEnv("DB_HOST", "localhost"),
+			Port:     getEnv("DB_PORT", "5432"),
+			Database: getEnv("DB_NAME", "telecom_platform"),
+			Username: getEnv("DB_USER", "postgres"),
+			Password: getEnv("DB_PASSWORD", "password"),
+			SSLMode:  getEnv("DB_SSLMODE", "disable"),
 		},
 		Redis: RedisConfig{
-			Host:     "localhost",
-			Port:     "6379",
-			Password: "",
-			DB:       0,
+			Host:     getEnv("REDIS_HOST", "localhost"),
+			Port:     getEnv("REDIS_PORT", "6379"),
+			Password: getEnv("REDIS_PASSWORD", ""),
+			DB:       getEnvInt("REDIS_DB", 0),
 		},
 		IMSI: IMSIConfig{
 			Prefix:  "20893", // France MCC+MNC
@@ -103,28 +121,28 @@ func LoadConfig() *Config {
 			MaxIMSI: 999999999,
 		},
 		ES2: ES2Config{
-			BaseURL:                  "https://smdp.example.com",
-			APIKey:                   "",
+			BaseURL:                  getEnv("ES2_BASE_URL", "https://smdp.example.com"),
+			APIKey:                   getEnv("ES2_API_KEY", ""),
 			InsecureSkipVerify:       true,
 			FunctionalityRequesterID: "telecom-platform",
 		},
 		Payment: PaymentConfig{
-			Provider:            "stripe",
-			StripeAPIKey:        "",
-			StripeWebhookSecret: "",
+			Provider:            getEnv("PAYMENT_PROVIDER", "stripe"),
+			StripeAPIKey:        getEnv("STRIPE_API_KEY", ""),
+			StripeWebhookSecret: getEnv("STRIPE_WEBHOOK_SECRET", ""),
 		},
 		ChargingEngine: ChargingEngineConfig{
-			BaseURL: "http://localhost:3001",
+			BaseURL: getEnv("CHARGING_ENGINE_URL", "http://localhost:3001"),
 			Timeout: 10 * time.Second,
 		},
 		InfluxDB: InfluxDBConfig{
-			URL:    "http://localhost:8086",
-			Token:  "",
-			Org:    "telecom",
-			Bucket: "telecom",
+			URL:    getEnv("INFLUXDB_URL", "http://localhost:8086"),
+			Token:  getEnv("INFLUXDB_TOKEN", ""),
+			Org:    getEnv("INFLUXDB_ORG", "telecom"),
+			Bucket: getEnv("INFLUXDB_BUCKET", "telecom"),
 		},
 		Auth: AuthConfig{
-			JWTSecret: "change-me-in-production",
+			JWTSecret: getEnv("JWT_SECRET", "change-me-in-production"),
 		},
 	}
 }