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-hal/ld/esp32/rom/esp32.rom.eco3.ld

@@ -0,0 +1,10 @@
+/*
+ESP32 ECO3 ROM address table
+Secure Boot Version 2 API's imported from the ROM
+*/
+PROVIDE ( ets_secure_boot_verify_signature = 0x4006543c);
+PROVIDE ( ets_secure_boot_verify_boot_bootloader = 0x400655ec);
+PROVIDE ( ets_use_secure_boot_v2 = 0x4000f8d4);
+PROVIDE ( ets_rsa_pss_verify = 0x40065310);
+PROVIDE ( ets_mgf1_sha256 = 0x400651a8);
+PROVIDE ( ets_emsa_pss_verify = 0x4006520c);