fix(ui): actionable toasts linger, and a dead hotkey shows in the sidebar

Every toast auto-dismissed after 2.8 s — fine for a success receipt, too
short to read AND act on an error. Errors and warnings now stay 10 s and can
be clicked away; success is unchanged.

The hotkey-conflict warning also needed a trace outside the toast: the ⚠ in
Settings only helps someone who opens the panel. A dot on the sidebar Settings
entry (plus a tooltip) is now the cue in the main UI that a combo is dead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.js

@@ -1016,7 +1016,16 @@ function toast(msg, type) {
     t.className = 'toast is-' + type;
     t.textContent = msg;
     container.appendChild(t);
-    setTimeout(() => t.remove(), 2800);
+    // A success toast is a receipt — 2.8 s is plenty. An error or warning is
+    // something the user has to READ and usually act on, and 2.8 s isn't
+    // enough for either, so those linger and can be clicked away early.
+    const actionable = (type === 'error' || type === 'warning');
+    if (actionable) {
+        t.classList.add('is-dismissable');
+        t.title = 'Click to dismiss';
+        t.addEventListener('click', () => t.remove());
+    }
+    setTimeout(() => t.remove(), actionable ? 10000 : 2800);
 }
 
 // ============================================================