refactor(config): 移除环境变量依赖，统一使用 Provider 配置系统

- 移除 .env.example 文件
- 简化 resolveApiKey 函数，只从配置文件读取 API Key
- 重构 loadConfig/loadVisionConfig/loadSummaryConfig 使用 ProviderRegistry
- 更新测试以 mock Provider 系统

packages/core/src/provider/registry.ts

@@ -126,7 +126,7 @@ export class ProviderRegistry {
     this.ensureInitialized();
     return Array.from(this.providers.entries()).map(([id, provider]) => {
       const config = this.configs.get(id);
-      const apiKey = resolveApiKey(config, provider.info.apiKeyEnvVar);
+      const apiKey = resolveApiKey(config);
       const customModels = config?.customModels ?? [];
 
       return {
@@ -165,7 +165,7 @@ export class ProviderRegistry {
     if (!provider) return undefined;
 
     const config = this.configs.get(id);
-    const apiKey = resolveApiKey(config, provider.info.apiKeyEnvVar);
+    const apiKey = resolveApiKey(config);
 
     return {
       id,
@@ -355,7 +355,7 @@ export class ProviderRegistry {
     }
 
     const config = this.configs.get(providerId);
-    const resolvedApiKey = apiKey ?? resolveApiKey(config, provider.info.apiKeyEnvVar);
+    const resolvedApiKey = apiKey ?? resolveApiKey(config);
 
     if (!resolvedApiKey && !provider.info.baseUrl?.includes('localhost')) {
       return { success: false, error: 'API key not configured' };
@@ -390,7 +390,7 @@ export class ProviderRegistry {
     }
 
     const config = this.configs.get(providerId);
-    const apiKey = options?.apiKey ?? resolveApiKey(config, provider.info.apiKeyEnvVar);
+    const apiKey = options?.apiKey ?? resolveApiKey(config);
     const baseUrl = options?.baseUrl ?? config?.baseUrl ?? provider.info.baseUrl;
 
     if (!apiKey) {