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/EditCredentialPage.tsx

@@ -23,7 +23,7 @@ export function EditCredentialPage() {
   useEffect(() => {
     if (!id) return;
     credentials
-      .get(Number(id))
+      .get(id)
       .then((c) => {
         setCredential(c);
         setName(c.name);
@@ -52,7 +52,7 @@ export function EditCredentialPage() {
     setSaving(true);
     setError(null);
     try {
-      await credentials.update(Number(id), {
+      await credentials.update(id!, {
         name: name.trim(),
         data: data.trim() || null,
       });