fix(cropper): professional permission-denied page

Centered card with navbar, lock icon, sans-serif stack (error pages
previously rendered in the browser default serif), and action-aware
copy: permission denial offers only 'Back to Tools' instead of a
pointless 'Try again'; auth failures keep Try again + Back to Tools.

tools/public/assets/style.css

@@ -21,6 +21,7 @@
 
 html, body { height: 100%; }
 body.app {
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
   background:
     radial-gradient(1200px 400px at 80% -10%, rgba(59, 79, 216, 0.08), transparent 60%),
     var(--bg);
@@ -31,6 +32,7 @@ body.app {
   flex-direction: column;
 }
 [v-cloak] { display: none; }
+a { text-decoration: none; }
 
 /* ── navbar ─────────────────────────────────────────────── */
 .nav {
@@ -60,7 +62,7 @@ body.app {
 
 /* ── layout ─────────────────────────────────────────────── */
 main.container { flex: 1 0 auto; }
-.narrow { max-width: 560px; }
+.narrow { max-width: 560px; margin-left: auto; margin-right: auto; }
 .center-v { display: flex; flex-direction: column; justify-content: center; min-height: 70vh; }
 .page-head { margin: 2.2rem 0 1.4rem; display: flex; align-items: flex-end; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
 .page-head h1 { font-size: 1.45rem; font-weight: 700; margin: 0; letter-spacing: -0.01em; }
@@ -113,7 +115,8 @@ label { font-weight: 600; font-size: 13px; color: var(--ink); margin-bottom: 0.3
 select.form-control { appearance: auto; }
 
 /* ── buttons ────────────────────────────────────────────── */
-.btn { border-radius: 10px; font-weight: 600; font-size: 14px; padding: 0.55rem 1.1rem; border: 1px solid transparent; }
+.btn { border-radius: 10px; font-weight: 600; font-size: 14px; padding: 0.55rem 1.1rem; border: 1px solid transparent; text-decoration: none; }
+a.btn:hover, a.btn:focus { text-decoration: none; }
 .btn:focus { box-shadow: 0 0 0 3px rgba(59, 79, 216, 0.18); }
 .btn-primary { background: var(--brand); border-color: var(--brand); color: #fff; }
 .btn-primary:hover, .btn-primary:focus { background: var(--brand-dark); border-color: var(--brand-dark); color: #fff; }