ArduinoNRF 0.3.5

Release 0.3.5 starts the official Nordic Zigbee sidecar path for nRF52840.\n\nHighlights:\n- Adds nCS Zigbee R23 sidecar bootstrap tools under hardware/arduinonrf/nrf52/tools/ncs_zigbee.\n- Records board1/ProMicro + J-Link as the first onboard Zigbee validation target.\n- Adds official stack and RADIO ownership policy docs.\n- Updates Zigbee docs to distinguish the official onboard sidecar path from the existing external CC2530 Arduino-sketch path.\n\nValidation:\n- PowerShell scripts parse successfully.\n- JSON pins/board metadata parse successfully.\n- Sidecar check-only mode ran without downloads or flashing.\n- package_arduinonrf_index.json validates and points to this release asset.\n\nKnown environment note:\n- Current machine has nRF Connect Desktop 5.3.1 installed, but west was not found on PATH during check-only discovery; install/activate the nRF Connect SDK toolchain before building nCS Zigbee firmware.