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/esp32h2/memory.x

@@ -0,0 +1,34 @@
+MEMORY
+{
+     /* MEMORY_MAP = [
+        [0x00000000, 0x00010000, "PADDING"],
+        [0x42800000, 0x43000000, "DROM"],
+        [0x40800000, 0x40850000, "RAM"],
+        [0x40800000, 0x40850000, "BYTE_ACCESSIBLE"],
+        [0x4001С400, 0x40020000, "DROM_MASK"],
+        [0x40000000, 0x4001С400, "ROM_MASK"],
+        [0x42000000, 0x42800000, "ROM"],
+        [0x40800000, 0x40850000, "RAM"],
+        [0x50000000, 0x50001000, "RTC_RAM"],
+        [0x50000000, 0x50001000, "RTC_RAM"],
+        [0x600FE000, 0x60100000, "MEM_INTERNAL2"],
+    ] */
+
+
+    /* 320K of on soc RAM, 16K reserved for cache */
+    /* Instruction and Data RAM 
+    0x4083EFD0 = 2nd stage bootloader iram_loader_seg start address
+    see https://github.com/espressif/esp-idf/blob/03414a15508036c8fc0f51642aed7a264e9527df/components/esp_system/ld/esp32h2/memory.ld.in#L26
+    */
+    RAM : ORIGIN = 0x40800000, LENGTH = 0x3EFD0
+
+    /* memory available after the 2nd stage bootloader is finished */
+    dram2_seg ( RW )       : ORIGIN = ORIGIN(RAM) + LENGTH(RAM), len = 0x4084fee0 - (ORIGIN(RAM) + LENGTH(RAM))
+
+    /* External flash */
+    /* Instruction and Data ROM */
+    ROM : ORIGIN =   0x42000000, LENGTH = 0x400000
+
+    /* RTC fast memory (executable). Persists over deep sleep. */
+    RTC_FAST : ORIGIN = 0x50000000, LENGTH = 16K /*- ESP_BOOTLOADER_RESERVE_RTC*/
+}