Initial commit: RNodeTHV4 boundary mode firmware for Heltec V4

Bridges LoRa mesh and TCP/WiFi backbone networks using microReticulum.
Based on microReticulum_Firmware with boundary mode additions:
- BoundaryMode.h: State management and EEPROM persistence
- BoundaryConfig.h: WiFi captive portal for configuration
- TcpInterface.h: TCP backbone interface with HDLC framing
- Display.h: Custom OLED layout with network status indicators
- Transport/Identity library patches for embedded memory constraints

Console/source/s_sideband.md

@@ -0,0 +1,12 @@
+[title]: <> (Sideband)
+## Sideband
+Sideband is an LXMF client for Android, Linux, Windows and macOS. It has built-in support for communicating over RNodes, and many other mediums, such as Packet Radio, WiFi, I2P, or anything else Reticulum supports.
+
+Sideband also supports voice calls, file transfers, and exchanging messages through encrypted QR-codes on paper, or through messages embedded directly in lxm:// links.
+
+![Screenshot]({ASSET_PATH}gfx/sideband.webp)
+
+The installation files for the Sideband program is too large to be included on this RNode, but downloads for Linux, Android and macOS can be obtained from following sources:
+
+- The [Sideband page](https://unsigned.io/sideband/) on [unsigned.io](https://unsigned.io/)
+- The [GitHub release page for Sideband](https://github.com/markqvist/Sideband/releases/latest)