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/esp32c2/rom/esp32c2.rom.libgcc.ld

@@ -0,0 +1,113 @@
+/*
+ * SPDX-FileCopyrightText: 2021-2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* ROM function interface esp32c2.rom.libgcc.ld for esp32c2
+ *
+ *
+ * Generated from ./interface-esp32c2.yml md5sum c679b6ed5e9f0a9c3e7b93e5e0f2a1a3
+ *
+ * Compatible with ROM where ECO version equal or greater to 1.
+ *
+ * THIS FILE WAS AUTOMATICALLY GENERATED. DO NOT EDIT.
+ */
+
+/***************************************
+ Group libgcc
+ ***************************************/
+
+/* Functions */
+__absvdi2 = 0x400008a8;
+__absvsi2 = 0x400008ac;
+__adddf3 = 0x400008b0;
+__addsf3 = 0x400008b4;
+__addvdi3 = 0x400008b8;
+__addvsi3 = 0x400008bc;
+__ashldi3 = 0x400008c0;
+__ashrdi3 = 0x400008c4;
+__bswapdi2 = 0x400008c8;
+__bswapsi2 = 0x400008cc;
+__clear_cache = 0x400008d0;
+__clrsbdi2 = 0x400008d4;
+__clrsbsi2 = 0x400008d8;
+__clzdi2 = 0x400008dc;
+__clzsi2 = 0x400008e0;
+__cmpdi2 = 0x400008e4;
+__ctzdi2 = 0x400008e8;
+__ctzsi2 = 0x400008ec;
+__divdc3 = 0x400008f0;
+__divdf3 = 0x400008f4;
+__divdi3 = 0x400008f8;
+__divsc3 = 0x400008fc;
+__divsf3 = 0x40000900;
+__divsi3 = 0x40000904;
+__eqdf2 = 0x40000908;
+__eqsf2 = 0x4000090c;
+__extendsfdf2 = 0x40000910;
+__ffsdi2 = 0x40000914;
+__ffssi2 = 0x40000918;
+__fixdfdi = 0x4000091c;
+__fixdfsi = 0x40000920;
+__fixsfdi = 0x40000924;
+__fixsfsi = 0x40000928;
+__fixunsdfsi = 0x4000092c;
+__fixunssfdi = 0x40000930;
+__fixunssfsi = 0x40000934;
+__floatdidf = 0x40000938;
+__floatdisf = 0x4000093c;
+__floatsidf = 0x40000940;
+__floatsisf = 0x40000944;
+__floatundidf = 0x40000948;
+__floatundisf = 0x4000094c;
+__floatunsidf = 0x40000950;
+__floatunsisf = 0x40000954;
+__gcc_bcmp = 0x40000958;
+__gedf2 = 0x4000095c;
+__gesf2 = 0x40000960;
+__gtdf2 = 0x40000964;
+__gtsf2 = 0x40000968;
+__ledf2 = 0x4000096c;
+__lesf2 = 0x40000970;
+__lshrdi3 = 0x40000974;
+__ltdf2 = 0x40000978;
+__ltsf2 = 0x4000097c;
+__moddi3 = 0x40000980;
+__modsi3 = 0x40000984;
+__muldc3 = 0x40000988;
+__muldf3 = 0x4000098c;
+__muldi3 = 0x40000990;
+__mulsc3 = 0x40000994;
+__mulsf3 = 0x40000998;
+__mulsi3 = 0x4000099c;
+__mulvdi3 = 0x400009a0;
+__mulvsi3 = 0x400009a4;
+__nedf2 = 0x400009a8;
+__negdf2 = 0x400009ac;
+__negdi2 = 0x400009b0;
+__negsf2 = 0x400009b4;
+__negvdi2 = 0x400009b8;
+__negvsi2 = 0x400009bc;
+__nesf2 = 0x400009c0;
+__paritysi2 = 0x400009c4;
+__popcountdi2 = 0x400009c8;
+__popcountsi2 = 0x400009cc;
+__powidf2 = 0x400009d0;
+__powisf2 = 0x400009d4;
+__subdf3 = 0x400009d8;
+__subsf3 = 0x400009dc;
+__subvdi3 = 0x400009e0;
+__subvsi3 = 0x400009e4;
+__truncdfsf2 = 0x400009e8;
+__ucmpdi2 = 0x400009ec;
+__udivdi3 = 0x400009f0;
+__udivmoddi4 = 0x400009f4;
+__udivsi3 = 0x400009f8;
+__udiv_w_sdiv = 0x400009fc;
+__umoddi3 = 0x40000a00;
+__umodsi3 = 0x40000a04;
+__unorddf2 = 0x40000a08;
+__unordsf2 = 0x40000a0c;
+__extenddftf2 = 0x40000a10;
+__trunctfdf2 = 0x40000a14;