feat(database): add DATABASE_CONFIG_FILE env override

Allow overriding default database.yaml paths via DATABASE_CONFIG_FILE
environment variable. When set, uses single specified file instead of
default ["database.yaml", "/vault/secrets/database.yaml"] search paths.

Maintains backward compatibility when env var not set.

database/config.go

@@ -1,6 +1,7 @@
 package database
 
 import (
+	"os"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
@@ -36,10 +37,20 @@ type ConfigOptions struct {
 	ConnMaxLifetime time.Duration
 }
 
+// getConfigFiles returns the list of config files to search for database configuration.
+// If DATABASE_CONFIG_FILE environment variable is set, it returns that single file.
+// Otherwise, it returns the default paths.
+func getConfigFiles() []string {
+	if configFile := os.Getenv("DATABASE_CONFIG_FILE"); configFile != "" {
+		return []string{configFile}
+	}
+	return []string{"database.yaml", "/vault/secrets/database.yaml"}
+}
+
 // DefaultConfigOptions returns the standard configuration options used by API package
 func DefaultConfigOptions() ConfigOptions {
 	return ConfigOptions{
-		ConfigFiles:          []string{"database.yaml", "/vault/secrets/database.yaml"},
+		ConfigFiles:          getConfigFiles(),
 		EnablePoolMonitoring: true,
 		PrometheusRegisterer: prometheus.DefaultRegisterer,
 		MaxOpenConns:         25,
@@ -51,7 +62,7 @@ func DefaultConfigOptions() ConfigOptions {
 // MonitorConfigOptions returns configuration options optimized for Monitor package
 func MonitorConfigOptions() ConfigOptions {
 	return ConfigOptions{
-		ConfigFiles:          []string{"database.yaml", "/vault/secrets/database.yaml"},
+		ConfigFiles:          getConfigFiles(),
 		EnablePoolMonitoring: false, // Monitor doesn't need metrics
 		PrometheusRegisterer: nil,   // No Prometheus dependency
 		MaxOpenConns:         10,