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-metadata/devices/esp32.toml

@@ -0,0 +1,76 @@
+[device]
+name  = "esp32"
+arch  = "xtensa"
+cores = "multi_core"
+
+peripherals = [
+    # Peripherals available in the PAC:
+    "aes",
+    "apb_ctrl",
+    "bb",
+    "dport",
+    "efuse",
+    "flash_encryption",
+    "frc_timer",
+    "gpio",
+    "gpio_sd",
+    "hinf",
+    "i2c0",
+    "i2c1",
+    "i2s0",
+    "i2s1",
+    "io_mux",
+    "ledc",
+    "mcpwm0",
+    "mcpwm1",
+    "nrx",
+    "pcnt",
+    "rmt",
+    "rng",
+    "rsa",
+    "rtc_cntl",
+    "rtc_i2c",
+    "rtc_io",
+    "sdhost",
+    "sens",
+    "sha",
+    "slc",
+    "slchost",
+    "spi0",
+    "spi1",
+    "spi2",
+    "spi3",
+    "timg0",
+    "timg1",
+    "twai0",
+    "uart0",
+    "uart1",
+    "uart2",
+    "uhci0",
+    "uhci1",
+]
+
+symbols = [
+    # Additional peripherals defined by us (the developers):
+    "adc",
+    "dac",
+    "pdma",
+    "phy",
+    "bt",
+    "wifi",
+    "psram",
+    "timg_timer1",
+    "touch",
+    "large_intr_status",
+
+    # ROM capabilities
+    "rom_crc_le",
+    "rom_crc_be",
+    "rom_md5_bsd",
+
+    # Wakeup SOC based on ESP-IDF:
+    "pm_support_ext0_wakeup",
+    "pm_support_ext1_wakeup",
+    "pm_support_touch_sensor_wakeup",
+    "ulp_supported",
+]