feat: add display UI with splash screen, dashboard, and RSSI sparkline

Implement full SSD1306 OLED display support:
- Splash screen on boot (1.5s) with project name, version, board
- Dashboard showing radio state, config, counters, RSSI/SNR
- RSSI history sparkline (64-sample ring buffer, 2px-wide bars)
- DisplayOn/DisplayOff host commands routed via dedicated channel
- Pure render functions against generic DrawTarget (no hardware coupling)
- Display on/off control bypasses radio task entirely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/esp-synopsys-usb-otg/README.md

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+[![crates.io](https://img.shields.io/crates/d/esp-synopsys-usb-otg.svg)](https://crates.io/crates/esp-synopsys-usb-otg)
+[![crates.io](https://img.shields.io/crates/v/esp-synopsys-usb-otg.svg)](https://crates.io/crates/esp-synopsys-usb-otg)
+
+# This is a fork of [synopsys-usb-otg](https://crates.io/crates/synopsys-usb-otg) with support for ESP32-Sx added - please use https://github.com/stm32-rs/synopsys-usb-otg when not targeting ESP32-Sx
+
+# `synopsys-usb-otg`
+
+> [usb-device](https://github.com/mvirkkunen/usb-device) implementation for Synopsys USB OTG IP cores.
+
+This project is a successor to the [great work](https://github.com/mvirkkunen/stm32f103xx-usb)
+started by [@mvirkkunen](https://github.com/mvirkkunen).
+
+## Supported microcontrollers
+
+* `STM32F429xx` (OTG_FS and OTG_HS in FS mode)
+* `STM32F401xx`
+* `STM32F446xx` (OTG_FS and OTG_HS in FS mode)
+* `STM32F723xx` (OTG_FS and OTG_HS with internal HS PHY)
+* `STM32H7xxxx` (OTG1_HS and OTG2_HS in FS mode, and OTG1_HS with external HS PHY)
+* And others...
+
+
+## Usage
+
+This driver is intended for use through a device hal library.
+Such hal library should implement `UsbPeripheral` for the corresponding USB peripheral object.
+This trait declares all the peripheral properties that may vary from one device family to the other.
+Additionally, hal should pass `fs` of `hs` feature to the `synopsys-usb-otg` library to
+define a peripheral type:
+* `fs` - for FullSpeed peripherals
+* `hs` - for HighSpeed peripherals
+
+Only one peripheral type can be selected at the moment.
+
+### ULPI Transciever Delay
+
+Some ULPI PHYs like the Microchip USB334x series require a delay between the ULPI register write that initiates
+the HS Chirp and the subsequent transmit command, otherwise the HS Chirp does not get executed and the deivce
+enumerates in FS mode. Some USB Link IP like those in the STM32H7 series support adding this delay to work with the
+affected PHYs. Enable the `xcvrdly` feature to add this delay.
+
+## Examples
+
+See the [usb-otg-workspace](https://github.com/Disasm/usb-otg-workspace) repo for different device-specific examples.