Natures: add the missing back link

Every other reference page (Move/Item/Ability detail) has a '‹ back'
link; NaturesView never got one, so the only way out was the phone's
back gesture or the bottom nav. Add the same lookup__nav link, pointing
at #/team since that's the page's only current entry point.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017Ve7HLspzeG2xDPtJQ8vmu

src/views/NaturesView.js

@@ -4,6 +4,7 @@ import { NATURES, STAT_LABEL } from '../data/natures.js';
 export function NaturesView() {
   const view = el('section', { class: 'view lookup' });
   view.append(
+    el('nav', { class: 'lookup__nav' }, el('a', { class: 'link', href: '#/team' }, '‹ Team')),
     el(
       'header',
       { class: 'view__header' },