fix(brain): give the Add Memory form a submit button and reliable Enter handling (#5830)

The Brain > Add tab rendered only a text input and category select with no
submit control, and Enter submission relied on a deprecated keypress
listener that is not guaranteed to fire, so the form could not be
submitted at all (#5828).

Add a labelled submit button styled like the neighbouring Skill Import
button (theme-io-btn, inline SVG icon), switch the Enter handler to
keydown with preventDefault, ignore IME composition, and pin both submit
paths with a source-level regression test.

Fixes #5828

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

static/app.js

@@ -1689,12 +1689,20 @@ function initializeEventListeners() {
   
   const newMemoryInput = el('new-memory-input');
   if (newMemoryInput) {
-    newMemoryInput.addEventListener('keypress', (e) => {
-      if (e.key === 'Enter') {
+    // keydown, not the deprecated keypress: keypress is not guaranteed to
+    // fire for Enter everywhere, which left the Add Memory form with no
+    // working submit path (#5828).
+    newMemoryInput.addEventListener('keydown', (e) => {
+      if (e.key === 'Enter' && !e.isComposing) {
+        e.preventDefault();
         memoryModule.addNewMemory();
       }
     });
   }
+  const newMemoryAddBtn = el('new-memory-add-btn');
+  if (newMemoryAddBtn) {
+    newMemoryAddBtn.addEventListener('click', () => memoryModule.addNewMemory());
+  }
 
 // Voice recording is handled by the dual-purpose send/mic button (see below)