Explicitly enable spellcheck on chat message textareas (#34)

Browsers already spellcheck a plain <textarea> by default (confirmed
in-browser: spellcheck read true on the composer with nothing
disabling it), but that's an implicit default rather than a guarantee
across every browser/PWA context. Set spellCheck explicitly on both
the composer and the message-edit textarea so it can't silently be
off somewhere it wasn't verified.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/Composer.tsx

@@ -220,6 +220,7 @@ export function Composer({ roomId, roomName, disabled, onSend }: ComposerProps)
           }}
           onKeyDown={handleKeyDown}
           placeholder={disabled ? (online ? 'Connecting…' : "You're offline") : `Message #${roomName}`}
+          spellCheck
         />
         <button
           type="button"

frontend/src/components/MessageList.tsx

@@ -149,6 +149,7 @@ export function MessageList({ roomId, messages, members, onEdit, onReact }: Mess
                     if (e.key === 'Escape') setEditingId(null)
                   }}
                   onBlur={() => commitEdit(msg.id)}
+                  spellCheck
                 />
               ) : (
                 <>