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>

tools/make_webui_screenshots.py

@@ -0,0 +1,91 @@
+"""Saves screenshots of the web UI tabs in Pictures/web-ui/, with Microsoft Edge (or Chrome)
+in headless mode.
+
+    python tools/make_webui_screenshots.py [ESP32 address, default 10.1.1.198]
+
+Each tab is opened by its address (http://<ESP32>/#settings); the page editor with
+#pages/<page name>. Edge runs with its own temporary profile. Only the Python standard
+library is used.
+"""
+
+import json
+import os
+import shutil
+import subprocess
+import sys
+import tempfile
+import urllib.parse
+import urllib.request
+
+ESP = 'http://' + (sys.argv[1] if len(sys.argv) > 1 else '10.1.1.198')
+OUT = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), 'Pictures', 'web-ui')
+BROWSERS = [
+    r'C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe',
+    r'C:\Program Files\Microsoft\Edge\Application\msedge.exe',
+    r'C:\Program Files\Google\Chrome\Application\chrome.exe',
+    'microsoft-edge', 'google-chrome', 'chromium',
+]
+WIDTH = 1000
+# File name, address part, window height
+SHOTS = [
+    ('show', 'show', 2150),
+    ('pages', 'pages/Weer', 3000), # the page list and the editor (tall: nothing has to scroll)
+    ('schedule', 'schedule', 1150),
+    ('stopwatch', 'stopwatch', 560),
+    ('bitmaps', 'bitmaps', 1600),
+    ('draw', 'draw', 820),
+    ('settings', 'settings', 1550),
+    ('home-assistant', 'ha', 780),
+    ('system', 'system', 1080),
+]
+
+
+def browser():
+    for b in BROWSERS:
+        path = shutil.which(b) or (b if os.path.exists(b) else None)
+        if path:
+            return path
+    sys.exit('No Edge or Chrome found')
+
+
+def read_ha_values():
+    """Reads the Home Assistant values of all pages, so the previews show them"""
+    with urllib.request.urlopen(ESP + '/api/pages', timeout=20) as r:
+        pages = json.loads(r.read())['pages']
+    for entity in {(e['entity'], e.get('attribute', '')) for p in pages for e in p['page']['elements'] if e.get('entity')}:
+        query = urllib.parse.urlencode({'entity': entity[0], 'attribute': entity[1]})
+        try:
+            urllib.request.urlopen(ESP + '/api/ha/value?' + query, timeout=10).read()
+        except Exception:
+            pass
+
+
+def shoot(exe, profile, path, address, height):
+    for attempt in range(3):
+        try:
+            subprocess.run([exe, '--headless=new', '--disable-gpu', '--hide-scrollbars', '--user-data-dir=' + profile,
+                            '--window-size=%d,%d' % (WIDTH, height), '--virtual-time-budget=20000',
+                            '--screenshot=' + path, address],
+                           stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL, timeout=90)
+            return True
+        except subprocess.TimeoutExpired:
+            pass  # the browser hung: try again
+    return False
+
+
+def main():
+    exe = browser()
+    read_ha_values()
+    os.makedirs(OUT, exist_ok=True)
+    profile = tempfile.mkdtemp(prefix='flipdot-edge-')
+    try:
+        for name, hash_part, height in SHOTS:
+            path = os.path.join(OUT, name + '.png')
+            ok = shoot(exe, profile, path, ESP + '/#' + hash_part, height)
+            print(name, os.path.getsize(path) if ok and os.path.exists(path) else 'failed')
+    finally:
+        shutil.rmtree(profile, ignore_errors=True)
+
+
+if __name__ == '__main__':
+    main()