security: 安全审计修复 - API Key清理 + JWT改为HttpOnly Cookie

- API Key: run.md/.env/seed_model_providers.sql 中明文Key替换为占位符
- 认证: JWT从localStorage迁移到HttpOnly Cookie，移除后端body返回token
- 前端: api.ts/knowledge/page.tsx/auth.ts 全面改用Cookie认证
- postcss XSS: package.json添加overrides强制升级到8.5.15
- gitignore: 添加server/.env和.env排除规则
- lint: 移除tenant.go中未使用的roleKey常量
- 文档: 新增docs/security-audit-report.md和hardware-requirements.md

server/pkg/tenant/tenant.go

@@ -11,9 +11,8 @@ import (
 type contextKey string
 
 const (
-	orgIDKey   contextKey = "org_id"
-	userIDKey  contextKey = "user_id"
-	roleKey    contextKey = "role"
+	orgIDKey  contextKey = "org_id"
+	userIDKey contextKey = "user_id"
 )
 
 // WithOrgID stores the organization ID in context.