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/zerocopy/benches/try_read_from_suffix.x86-64

@@ -0,0 +1,18 @@
+bench_try_read_from_suffix_static_size:
+	mov eax, 49345
+	cmp rsi, 6
+	jb .LBB5_2
+	mov eax, dword ptr [rdi + rsi - 6]
+	movzx ecx, word ptr [rdi + rsi - 2]
+	shl rcx, 32
+	or rcx, rax
+	movzx edx, cx
+	xor eax, eax
+	cmp edx, 49344
+	cmovne rcx, rsi
+	sete al
+	and rcx, -65536
+	xor rax, 49345
+	or rax, rcx
+.LBB5_2:
+	ret