fix(ui): don't submit chat message on Enter during IME composition (#1091)

CJK and other IME users confirm a candidate from the input-method popup by pressing Enter. The chat composer and the in-place message editor each bind a keydown handler that treats Enter (without Shift) as "submit", but they did not exclude the composition state. Pressing Enter to accept an IME candidate therefore sent the half-composed text (e.g. a stray "ce's") instead of just confirming the candidate.

These textareas intentionally hijack Enter to submit (Enter sends, Shift+Enter inserts a newline), which bypasses the browser's native form submission and the IME guard that comes with it, so the guard has to be re-added explicitly.

Add '&& !e.isComposing' to the three Enter-to-submit handlers: static/app.js (the main composer's button-submit path and its send/new-chat path) and static/js/chat.js (the editor for an already-sent message). Normal Enter (isComposing false) still submits; Shift+Enter still inserts a newline.

Tested: node --check on both files; manually verified with a Chinese IME that pressing Enter to pick a candidate no longer sends, and a message is sent only after composition ends.

static/js/chat.js

@@ -3424,7 +3424,7 @@ import createResearchSynapse from './researchSynapse.js';
 
     // Also submit on Enter (without shift)
     editor.addEventListener('keydown', (e) => {
-      if (e.key === 'Enter' && !e.shiftKey) {
+      if (e.key === 'Enter' && !e.shiftKey && !e.isComposing) {
         e.preventDefault();
         saveBtn.click();
       }