feat(dashboard): add REGION env variable support

- Enable REGION environment variable to control regional config overrides
- Prioritize RUNTIME_ENV and REGION over file-based configuration
- Supports: RUNTIME_ENV=prod|sit and REGION=cn|global|default
- Loads from dashboard/config/runtime-service-config.{env}.yaml
- Fixes configuration loading with Turbopack compatibility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

dashboard/server/runtime-loader.ts

@@ -260,9 +260,13 @@ export function readRuntimeEnvSettings(): RuntimeEnvSettings {
   if (runtimeEnv) {
     const environment = normalizeEnvironmentValue(runtimeEnv)
     if (environment) {
+      // 检查 REGION 环境变量
+      const regionEnv = process.env.REGION
+      const region = regionEnv ? normalizeRegionValue(regionEnv) || 'default' : 'default'
+
       runtimeEnvSettingsCache = {
         environment,
-        region: 'default',
+        region,
         detectedBy: 'env:RUNTIME_ENV',
       }
       return runtimeEnvSettingsCache
@@ -307,12 +311,14 @@ export function readRuntimeEnvSettings(): RuntimeEnvSettings {
       }
 
       const environment = normalizeEnvironmentValue(parsed.environment)
-      const region = normalizeRegionValue(parsed.region)
+      const regionEnv = process.env.REGION
+      const regionFromFile = normalizeRegionValue(parsed.region)
+      const region = regionEnv ? (normalizeRegionValue(regionEnv) || 'default') : (regionFromFile ?? 'default')
 
       if (environment) {
         runtimeEnvSettingsCache = {
           environment,
-          region: region ?? 'default',
+          region,
           detectedBy: candidate.detectedBy,
         }
         return runtimeEnvSettingsCache