fix: harden identity, live access, drafts and setup (review only)

Source-reviewed hardening changes and regression tests. UNBUILT / UNTESTED: not a deployable release. Go formatting, compilation, automated regression tests, full frontend validation and staging acceptance remain required. See docs/hardening/VALIDATION.md. Main remains the original clean snapshot; no upstream Git history imported.

internal/pkg/i18nx/locales/zh-CN.yml

@@ -1,3 +1,4 @@
+# Modified in the independent hardening fork; upstream notices retained.
 error.e0001: "AI Agent not found"
 error.e0002: "AI Agent 不存在"
 error.e0003: "AI Agent 不存在或已停用"
@@ -567,3 +568,12 @@ tool.graph.prepareTicketDraft.param.expectedOutcome: "用户期望的处理结
 tool.graph.prepareTicketDraft.param.currentAttempt: "当前已尝试过的处理步骤，可选。"
 error.setup.invalidQuickFixAction: "不支持的一键修复操作：%v"
 error.setup.authRequired: "请先登录以执行配置诊断或一键修复"
+
+error.setup.previewRequired: "应用更改前，请先预览设置并明确确认预览令牌。"
+error.setup.previewChanged: "预览后配置已更改。请重新预览后再应用。"
+error.setup.targetRequired: "请选择具体记录，或在对应设置中选择所需配置。"
+error.setup.targetUnavailable: "所选记录不可用、已删除或不符合条件，未进行恢复。"
+error.setup.persistenceFailed: "无法读取或保存设置配置，未提交不完整的修复。"
+error.setup.bypassUnsupported: "此诊断不支持绕过 AI。请检查仅人工路由，或单独测试 AI。"
+error.channel.configChanged: "渠道配置已更改。请重新加载并检查更改后再保存。"
+error.channel.configUpdateFailed: "无法保存渠道配置，请重试。"