feat(ssf): 托管机器凭据并支持动态恢复

Gateway 连接表单接收认证中心一次性交付的 machine Client 凭据，后端立即写入 SecretStore，数据库和公开响应只保留引用及公开 Client ID。SSF 管理 Token、Verification 和 RFC 7662 内省统一从动态凭据读取，支持现有连接无重启修复及进程重启恢复，环境变量仅保留为旧部署回退。\n\n验证：go test ./apps/api/...；pnpm nx test web；真实重启、OIDC 登录与 session-revoked 1.29 秒失效验收。

.env.example

@@ -33,6 +33,8 @@ OIDC_REQUIRED_SCOPES=gateway.access
 OIDC_JWKS_CACHE_TTL_SECONDS=300
 OIDC_ACCEPT_LEGACY_HS256=true
 OIDC_INTROSPECTION_ENABLED=false
+# Legacy/static fallback only. New SSF connections receive the machine
+# credential once in the web flow and persist it in the configured SecretStore.
 OIDC_INTROSPECTION_CLIENT_ID=
 OIDC_INTROSPECTION_CLIENT_SECRET=
 # SSF/CAEP is activated by the durable connection created in System Settings;