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/recovery/README.md

@@ -8,7 +8,7 @@ the clock firmware never change it. Its job: the ESP32 stays reachable, whatever
 to the clock firmware, so it never needs USB again.
 
 Installing it and using it as a user is described in the
-[main README](../../README.md#recovery-app). This file is about how it works.
+[documentation](../../docs/recovery.md). This file is about how it works.
 
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