Add LCD Gateway page; wire it into nav The ESP32-P4 + 10.1" MIPI-DSI touchscreen gateway (repo SplitFlapGatewayLCD) was undocumented. New LCD-Gateway.md mirrors Matrix-Gateway.md: the shared virtual-flap emulation and 237-flap reel, the Ethernet/PoE + touchscreen + no-RTC differences, canvas/effects, and timer/alarm double-tap dismissal. Wired in: _Sidebar (Build it), Home (branches + page index + release notes), Choosing-a-Configuration (both no-hardware callouts now name it too).