refactor: simplify config to prefer env vars

Configuration now prefers environment variables over config.yaml values.
Each config field has a corresponding env var (DBURL, PORT, DEBUG, etc.)
that takes precedence when set. The config.yaml fallback is preserved
for development convenience.

closes #10

internal/config/config.go

@@ -4,19 +4,16 @@ import (
 	"fmt"
 	"log/slog"
 	"os"
+	"strconv"
+	"strings"
 
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/globals"
 	"sneak.berlin/go/webhooker/internal/logger"
 	pkgconfig "sneak.berlin/go/webhooker/pkg/config"
 
-	// spooky action at a distance!
-	// this populates the environment
-	// from a ./.env file automatically
-	// for development configuration.
-	// .env contents should be things like
-	// `DBURL=postgres://user:pass@.../`
-	// (without the backticks, of course)
+	// Populates the environment from a ./.env file automatically for
+	// development configuration. Kept in one place only (here).
 	_ "github.com/joho/godotenv/autoload"
 )
 
@@ -64,6 +61,40 @@ func (c *Config) IsProd() bool {
 	return c.Environment == EnvironmentProd
 }
 
+// envString returns the env var value if set, otherwise falls back to pkgconfig.
+func envString(envKey, configKey string) string {
+	if v := os.Getenv(envKey); v != "" {
+		return v
+	}
+	return pkgconfig.GetString(configKey)
+}
+
+// envSecretString returns the env var value if set, otherwise falls back to pkgconfig secrets.
+func envSecretString(envKey, configKey string) string {
+	if v := os.Getenv(envKey); v != "" {
+		return v
+	}
+	return pkgconfig.GetSecretString(configKey)
+}
+
+// envBool returns the env var value parsed as bool, otherwise falls back to pkgconfig.
+func envBool(envKey, configKey string) bool {
+	if v := os.Getenv(envKey); v != "" {
+		return strings.EqualFold(v, "true") || v == "1"
+	}
+	return pkgconfig.GetBool(configKey)
+}
+
+// envInt returns the env var value parsed as int, otherwise falls back to pkgconfig.
+func envInt(envKey, configKey string, defaultValue ...int) int {
+	if v := os.Getenv(envKey); v != "" {
+		if i, err := strconv.Atoi(v); err == nil {
+			return i
+		}
+	}
+	return pkgconfig.GetInt(configKey, defaultValue...)
+}
+
 // nolint:revive // lc parameter is required by fx even if unused
 func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 	log := params.Logger.Get()
@@ -80,30 +111,30 @@ func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 			EnvironmentDev, EnvironmentProd, environment)
 	}
 
-	// Set the environment in the config package
+	// Set the environment in the config package (for fallback resolution)
 	pkgconfig.SetEnvironment(environment)
 
-	// Load configuration values
+	// Load configuration values — env vars take precedence over config.yaml
 	s := &Config{
-		DBURL:            pkgconfig.GetString("dburl"),
-		Debug:            pkgconfig.GetBool("debug"),
-		MaintenanceMode:  pkgconfig.GetBool("maintenanceMode"),
-		DevelopmentMode:  pkgconfig.GetBool("developmentMode"),
-		DevAdminUsername: pkgconfig.GetString("devAdminUsername"),
-		DevAdminPassword: pkgconfig.GetString("devAdminPassword"),
-		Environment:      pkgconfig.GetString("environment", environment),
-		MetricsUsername:  pkgconfig.GetString("metricsUsername"),
-		MetricsPassword:  pkgconfig.GetString("metricsPassword"),
-		Port:             pkgconfig.GetInt("port", 8080),
-		SentryDSN:        pkgconfig.GetSecretString("sentryDSN"),
-		SessionKey:       pkgconfig.GetSecretString("sessionKey"),
+		DBURL:            envString("DBURL", "dburl"),
+		Debug:            envBool("DEBUG", "debug"),
+		MaintenanceMode:  envBool("MAINTENANCE_MODE", "maintenanceMode"),
+		DevelopmentMode:  envBool("DEVELOPMENT_MODE", "developmentMode"),
+		DevAdminUsername: envString("DEV_ADMIN_USERNAME", "devAdminUsername"),
+		DevAdminPassword: envString("DEV_ADMIN_PASSWORD", "devAdminPassword"),
+		Environment:      environment,
+		MetricsUsername:  envString("METRICS_USERNAME", "metricsUsername"),
+		MetricsPassword:  envString("METRICS_PASSWORD", "metricsPassword"),
+		Port:             envInt("PORT", "port", 8080),
+		SentryDSN:        envSecretString("SENTRY_DSN", "sentryDSN"),
+		SessionKey:       envSecretString("SESSION_KEY", "sessionKey"),
 		log:              log,
 		params:           &params,
 	}
 
 	// Validate database URL
 	if s.DBURL == "" {
-		return nil, fmt.Errorf("database URL (dburl) is required")
+		return nil, fmt.Errorf("database URL (DBURL) is required")
 	}
 
 	// In production, require session key