Split the README into docs/ pages, add web UI screenshots

- README is the overview; web UI, pages, Home Assistant, how it works,
  wiring, Nano over WiFi and the recovery app have their own page in docs/.
- docs/web-ui.md has a screenshot of every tab, made with headless Edge by
  tools/make_webui_screenshots.py.
- The web UI opens a page in the editor with #pages/<name>. Version 2.7.2.
- The reply wire is fitted (flashing the Nano over WiFi works).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/esp32/web/web_page.h

@@ -549,6 +549,9 @@ function collect(){const s=JSON.parse(JSON.stringify(settings));
  if($('ha_pass').value)s.home_assistant.password=$('ha_pass').value;if($('ha_token').value)s.home_assistant.token=$('ha_token').value.trim();return s}
 async function saveSettings(){const r=await post('/api/settings',collect());settings=r.settings;fill();msg(r.restart?'Saved, restarting...':'Settings saved')}
 async function saveHa(){await saveSettings()}
-async function start(){settings=await api('/api/settings');fill();tab((location.hash||'#show').slice(1));pollScreen();pollStatus();loadLists()}
+// #tab, or #pages/<name> to open a page in the editor
+async function start(){settings=await api('/api/settings');fill();const[t,arg]=decodeURIComponent((location.hash||'#show').slice(1)).split('/');
+ tab(t);pollScreen();pollStatus();await loadLists();
+ if(t=='pages'&&arg){const pg=pageList.find(p=>same(p.name,arg));if(pg)peOpen(pg,pg.builtin)}}
 start();
 </script></body></html>)rawliteral";