Add touch-pad sync page

Speaker-Sync-%28Touch%29.md

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+# Speaker Sync (touch pads)
+
+JBL and Cardo have independent Bluetooth buffering, so one lags the other. Each
+**source board** has an adjustable delay (0-200 ms) you trim live, **by ear**, with
+two capacitive-touch pads. The value is saved to flash (survives power-cycles).
+
+| Pad | Pin    | Action                        |
+|-----|--------|-------------------------------|
+| +   | GPIO4  | tap = +5 ms, hold = ramp up   |
+| -   | GPIO27 | tap = -5 ms, hold = ramp down |
+
+- Attach a short wire or a bit of foil to GPIO4 and GPIO27 on each source board and
+  touch the end (a bare header pin is hard to trigger).
+- Raise the delay on whichever speaker is **early** until the two line up.
+- Touch threshold is ~40 (untouched reads ~115-130); adjust in firmware if your
+  pads read differently.
+
+**Why no Wi-Fi/phone UI:** Wi-Fi + Bluetooth-A2DP + the audio buffer exceed the
+classic ESP32's RAM and starve the Bluetooth stack (it won't connect to a speaker).
+So sync control is local capacitive touch instead of a web page.