feat(export-import): add yaml export/import with id upsert for credentials, snippets, and scenarios

- all entities export a kind field (credential/snippet/scenario) for safe type checking on import
- import upserts by id: overwrites if id exists, creates with explicit id otherwise
- scenario export now includes id and step ids; import deletes old steps before recreating
- add GET /:id/export and POST /import endpoints to credential and snippet controllers
- add UuidBadge ui component: shortens uuid to first+last 4 hex chars, tooltip, clipboard copy with animated ClipboardCheck icon pop
- apply UuidBadge across all entity id display sites (detail pages, card footers, table columns)
- add export/import buttons to CredentialsPage, SnippetsPage, CredentialDetailPage, SnippetDetailPage

client/src/pages/credential/CredentialDetailPage.tsx

@@ -1,10 +1,11 @@
 import { useEffect, useState } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
-import { Pencil, Trash2 } from 'lucide-react';
+import { Download, Pencil, Trash2 } from 'lucide-react';
+import { stringify as yamlStringify } from 'yaml';
 import { credentials } from '../../api';
 import type { Credential } from '../../api';
-import { Breadcrumbs, Button, Card, DescriptionList, Notification, Timestamp } from '../../ui';
+import { Breadcrumbs, Button, Card, DescriptionList, Notification, Timestamp, UuidBadge } from '../../ui';
 import styles from '../Page.module.css';
 
 export function CredentialDetailPage() {
@@ -18,7 +19,7 @@ export function CredentialDetailPage() {
   useEffect(() => {
     if (!id) return;
     credentials
-      .get(Number(id))
+      .get(id)
       .then(setCredential)
       .catch((err: Error) => setError(err.message))
       .finally(() => setLoading(false));
@@ -30,6 +31,18 @@ export function CredentialDetailPage() {
     navigate('/credentials');
   };
 
+  const handleExport = async () => {
+    if (!credential) return;
+    const data = await credentials.exportCredential(credential.id);
+    const blob = new Blob([yamlStringify(data)], { type: 'application/yaml' });
+    const url = URL.createObjectURL(blob);
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = `credential-${credential.name}.yaml`;
+    a.click();
+    URL.revokeObjectURL(url);
+  };
+
   return (
     <div>
       <div className={styles.pageToolbar}>
@@ -41,6 +54,10 @@ export function CredentialDetailPage() {
         />
         {credential && (
           <div className={styles.toolbarActions}>
+            <Button variant="secondary" size="sm" onClick={handleExport}>
+              <Download size={14} />
+              {t('credentials.action_export')}
+            </Button>
             <Button
               variant="secondary"
               size="sm"
@@ -74,7 +91,7 @@ export function CredentialDetailPage() {
             <DescriptionList
               layout="comfortable"
               items={[
-                { term: t('credentials.field_id'), detail: credential.id },
+                { term: t('credentials.field_id'), detail: <UuidBadge id={credential.id} /> },
                 {
                   term: t('credentials.field_last_used'),
                   detail: credential.lastUsedAt ? (