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>

CLAUDE.md

@@ -38,6 +38,10 @@ See README.md for the overview.
   `Serial` (UART0/USB) is free for debug output. Never write debug text to `Serial2`: the
   Nano runs lines that start with s/S/F/D/P/B/R/T/G/N/E as commands.
 - Open hardware TODOs are listed in the README `TODO` section. Update it when one is done.
+- The README is the overview; the documentation is in `docs/` (web UI, pages, Home
+  Assistant, how it works, wiring, Nano over WiFi, recovery app). Screenshots:
+  `tools/make_webui_screenshots.py` (headless Edge) and `tools/make_page_screenshots.py`
+  write `Pictures/web-ui/` and `Pictures/pages/`; run them again after UI changes.
 - `src/esp32/secrets.h` holds the real credentials and is gitignored. Never commit it.
   Add new secrets to `secrets.example.h` as placeholders.
 - The relay (ESP32 GPIO 13, `LOW` = on) powers both the panels and the Nano. Each time it
@@ -65,8 +69,8 @@ See README.md for the overview.
 - Flip time is stored in EEPROM as a magic word at address 0 and a `uint16_t` at
   address 2. Values outside 50–2000 µs are rejected.
 - The Nano only replies `READY` (at boot) and `ERR: ...`. There is no per-frame
-  acknowledgement. Whether the Nano's TX is wired to the ESP's RX is unconfirmed, so every
-  wait for a reply needs a timeout.
+  acknowledgement. The Nano's TX is wired to the ESP's RX (flashing over WiFi works), but
+  every wait for a reply still needs a timeout.
 - Unit tests: `pio test -e test_nano` runs `test/test_nano/` on the PC with the fakes in
   `test/mocks/` (Arduino, EEPROM, and a `BROSE9323` that records calls). It needs gcc on
   PATH (Strawberry Perl provides it at `C:\Strawberry\c\bin`). Add a test for every