Make repeated channel-monitor setup safer

Admins often recreate monitors with the same endpoint, model, and request settings. A server-side duplicate keeps the stored API key out of the browser, creates a disabled copy for review, and uses stable operation identity to recover ambiguous retries without creating extra rows.

Constraint: Stored monitor API keys must never be returned to the browser
Constraint: Applying a request template must preserve internal duplicate recovery metadata
Rejected: Rebuild the monitor from list data | list responses only contain a masked API key
Rejected: Copy runtime state and history | a duplicate should start as an unverified configuration
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep duplicated monitors disabled until an administrator reviews and enables them
Tested: Go unit tests for repository, service, and admin handler; integration-tag compile; go vet; golangci-lint v2.9; frontend Vitest, ESLint, typecheck, production build; Playwright duplicate flow
Not-tested: PostgreSQL container integration locally because Docker is unavailable; CI will execute the database-backed suite

frontend/src/i18n/locales/en/admin/channels.ts

@@ -479,6 +479,11 @@ export default {
       runNow: 'Run Now',
       runSuccess: 'Check completed',
       runFailed: 'Check failed',
+      duplicate: 'Duplicate',
+      duplicating: 'Duplicating',
+      duplicateSuccess: 'Monitor duplicated as "{name}" and disabled. Review its configuration before enabling it.',
+      duplicateFailed: 'Failed to duplicate monitor',
+      duplicateKeyUnavailable: 'The API key cannot be decrypted. Re-enter it before duplicating this monitor.',
       apiKeyDecryptFailed: 'API Key decryption failed. Please re-edit this monitor with a fresh key.',
       createSuccess: 'Monitor created',
       updateSuccess: 'Monitor updated',

frontend/src/i18n/locales/zh/admin/channels.ts

@@ -479,6 +479,11 @@ export default {
       runNow: '立即检测',
       runSuccess: '检测完成',
       runFailed: '检测失败',
+      duplicate: '复制',
+      duplicating: '复制中',
+      duplicateSuccess: '监控已复制为「{name}」，已默认停用，请确认配置后再启用',
+      duplicateFailed: '复制监控失败',
+      duplicateKeyUnavailable: 'API Key 无法解密，请先编辑并重新填写 Key 后再复制',
       apiKeyDecryptFailed: 'API Key 解密失败，请重新编辑该监控并填入新的 Key',
       createSuccess: '监控创建成功',
       updateSuccess: '监控更新成功',