feat(auth): aggregate OAuth 支持环境变量回退配置，默认 LOGIN_TYPE=wx

- oauth-strategies.ts: loadAggregateSettings() DB 未配置时回退读取 process.env.AGGREGATE_OAUTH_*，自动启用
- .env.example: AGGREGATE_OAUTH_LOGIN_TYPE 默认改为 wx，补充 auxx.cn 示例注释

server/utils/oauth-strategies.ts

@@ -270,7 +270,33 @@ async function loadAggregateSettings() {
     .from(systemSettings)
     .orderBy(asc(systemSettings.id))
     .limit(1)
-  return row[0] ?? null
+  const base = row[0] ?? null
+  const envAppId = process.env.AGGREGATE_OAUTH_APP_ID
+  const envAppKey = process.env.AGGREGATE_OAUTH_APP_KEY
+  const envLoginType = process.env.AGGREGATE_OAUTH_LOGIN_TYPE
+  const envEndpoint = process.env.AGGREGATE_OAUTH_ENDPOINT
+  const hasEnvConfig = !!(envAppId && envAppKey && envEndpoint)
+  const dbEnabled = base?.aggregateOAuthEnabled
+  const dbHasConfig = !!(
+    base?.aggregateOAuthAppId &&
+    base?.aggregateOAuthAppKey &&
+    base?.aggregateOAuthEndpoint
+  )
+  const enabled = Boolean(dbEnabled ?? hasEnvConfig)
+  const appId = (base?.aggregateOAuthAppId || envAppId || '') as string
+  const appKey = (base?.aggregateOAuthAppKey || envAppKey || '') as string
+  const loginType = ((base?.aggregateOAuthLoginType as string) || envLoginType || '') as string
+  const endpoint = ((base?.aggregateOAuthEndpoint as string) || envEndpoint || '') as string
+
+  return {
+    aggregateOAuthEnabled: enabled && !!(appId && appKey && endpoint),
+    aggregateOAuthAppId: appId,
+    aggregateOAuthAppKey: appKey,
+    aggregateOAuthLoginType: loginType,
+    aggregateOAuthEndpoint: endpoint,
+    _dbHasConfig: dbHasConfig,
+    _hasEnvConfig: hasEnvConfig
+  } as any
 }
 
 function normalizeEndpoint(endpoint: string): string {