feat: improve upload admin workflow

Add users.is_admin SQLite migration for promoted admins.

Support curl PUT request uploads, save uploads into admin file-manager paths, default 25 GiB uploads, tabbed UI, and local dev preview.

nextjs/app/%5Frequest/[id]/page.js

@@ -110,7 +110,7 @@ export default async function UploadRequestPage({ params, searchParams }) {
       </section>
 
       {state === 'open' ? (
-        <section className="panel panel-spotlight">
+        <section className="panel">
           <h2>Datei hochladen</h2>
           <form
             className="form-grid"
@@ -132,6 +132,11 @@ export default async function UploadRequestPage({ params, searchParams }) {
               Datei senden
             </button>
           </form>
+
+          <details className="help-box">
+            <summary>Upload per curl</summary>
+            <pre><code>{`curl -T ./datei.pdf -H 'X-File-Name: datei.pdf' 'https://HOST/_request/${requestEntry.id}/upload'`}</code></pre>
+          </details>
         </section>
       ) : null}