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/esp32c6.toml

@@ -0,0 +1,98 @@
+[device]
+name  = "esp32c6"
+arch  = "riscv"
+cores = "single_core"
+
+peripherals = [
+    # Peripherals available in the PAC:
+    "aes",
+    "apb_saradc",
+    "assist_debug",
+    "atomic",
+    "dma",
+    "ds",
+    "ecc",
+    "efuse",
+    "extmem",
+    "gpio",
+    "gpio_sd",
+    "hinf",
+    "hmac",
+    "hp_apm",
+    "hp_sys",
+    "i2c0",
+    "i2s0",
+    "interrupt_core0",
+    "intpri",
+    "io_mux",
+    "ledc",
+    "lp_ana",
+    "lp_aon",
+    "lp_apm",
+    "lp_apm0",
+    "lp_clkrst",
+    "lp_i2c0",
+    "lp_i2c_ana_mst",
+    "lp_io",
+    "lp_peri",
+    "lp_tee",
+    "lp_timer",
+    "lp_uart",
+    "lp_wdt",
+    "mcpwm0",
+    "mem_monitor",
+    "otp_debug",
+    "parl_io",
+    "pau",
+    "pcnt",
+    "pcr",
+    "pmu",
+    "rmt",
+    "rng",
+    "rsa",
+    "sha",
+    "slchost",
+    "soc_etm",
+    "spi0",
+    "spi1",
+    "spi2",
+    "systimer",
+    "tee",
+    "timg0",
+    "timg1",
+    "trace0",
+    "twai0",
+    "twai1",
+    "uart0",
+    "uart1",
+    "uhci0",
+    "usb_device",
+]
+
+symbols = [
+    # Additional peripherals defined by us (the developers):
+    "adc",
+    "assist_debug_sp_monitor",
+    "assist_debug_region_monitor",
+    "gdma",
+    "large_intr_status",
+    "plic",
+    "phy",
+    "bt",
+    "wifi",
+    "ieee802154",
+    "lp_core",
+
+    # ROM capabilities
+    "rom_crc_le",
+    "rom_crc_be",
+    "rom_md5_bsd",
+
+    # Wakeup SOC based on ESP-IDF:
+    "pm_support_wifi_wakeup",
+    "pm_support_beacon_wakeup",
+    "pm_support_bt_wakeup",
+    "gpio_support_deepsleep_wakeup",
+    "uart_support_wakeup_int",
+    "pm_support_ext1_wakeup",
+]