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.libgcc.ld

@@ -0,0 +1,94 @@
+/* Unlike other ROM functions which are exported using PROVIDE, which declares
+   weak symbols, these libgcc functions are exported using assignment,
+   which declares strong symbols. This is done so that ROM functions are always
+   used instead of the ones provided by libgcc.a.
+*/
+
+__absvdi2 = 0x4006387c;
+__absvsi2 = 0x40063868;
+__adddf3 = 0x40002590;
+__addsf3 = 0x400020e8;
+__addvdi3 = 0x40002cbc;
+__addvsi3 = 0x40002c98;
+__ashldi3 = 0x4000c818;
+__ashrdi3 = 0x4000c830;
+__bswapdi2 = 0x40064b08;
+__bswapsi2 = 0x40064ae0;
+__clrsbdi2 = 0x40064b7c;
+__clrsbsi2 = 0x40064b64;
+__clzdi2 = 0x4000ca50;
+__clzsi2 = 0x4000c7e8;
+__cmpdi2 = 0x40063820;
+__ctzdi2 = 0x4000ca64;
+__ctzsi2 = 0x4000c7f0;
+__divdc3 = 0x400645a4;
+__divdf3 = 0x40002954;
+__divdi3 = 0x4000ca84;
+__divsi3 = 0x4000c7b8;
+__eqdf2 = 0x400636a8;
+__eqsf2 = 0x40063374;
+__extendsfdf2 = 0x40002c34;
+__ffsdi2 = 0x4000ca2c;
+__ffssi2 = 0x4000c804;
+__fixdfdi = 0x40002ac4;
+__fixdfsi = 0x40002a78;
+__fixsfdi = 0x4000244c;
+__fixsfsi = 0x4000240c;
+__fixunsdfsi = 0x40002b30;
+__fixunssfdi = 0x40002504;
+__fixunssfsi = 0x400024ac;
+__floatdidf = 0x4000c988;
+__floatdisf = 0x4000c8c0;
+__floatsidf = 0x4000c944;
+__floatsisf = 0x4000c870;
+__floatundidf = 0x4000c978;
+__floatundisf = 0x4000c8b0;
+__floatunsidf = 0x4000c938;
+__floatunsisf = 0x4000c864;
+__gcc_bcmp = 0x40064a70;
+__gedf2 = 0x40063768;
+__gesf2 = 0x4006340c;
+__gtdf2 = 0x400636dc;
+__gtsf2 = 0x400633a0;
+__ledf2 = 0x40063704;
+__lesf2 = 0x400633c0;
+__lshrdi3 = 0x4000c84c;
+__ltdf2 = 0x40063790;
+__ltsf2 = 0x4006342c;
+__moddi3 = 0x4000cd4c;
+__modsi3 = 0x4000c7c0;
+__muldc3 = 0x40063c90;
+__muldf3 = 0x4006358c;
+__muldi3 = 0x4000c9fc;
+__mulsf3 = 0x400632c8;
+__mulsi3 = 0x4000c7b0;
+__mulvdi3 = 0x40002d78;
+__mulvsi3 = 0x40002d60;
+__nedf2 = 0x400636a8;
+__negdf2 = 0x400634a0;
+__negdi2 = 0x4000ca14;
+__negsf2 = 0x400020c0;
+__negvdi2 = 0x40002e98;
+__negvsi2 = 0x40002e78;
+__nesf2 = 0x40063374;
+__nsau_data = 0x3ff96544;
+__paritysi2 = 0x40002f3c;
+__popcount_tab = 0x3ff96544;
+__popcountdi2 = 0x40002ef8;
+__popcountsi2 = 0x40002ed0;
+__powidf2 = 0x400638e4;
+__subdf3 = 0x400026e4;
+__subsf3 = 0x400021d0;
+__subvdi3 = 0x40002d20;
+__subvsi3 = 0x40002cf8;
+__truncdfsf2 = 0x40002b90;
+__ucmpdi2 = 0x40063840;
+__udiv_w_sdiv = 0x40064bec;
+__udivdi3 = 0x4000cff8;
+__udivmoddi4 = 0x40064bf4;
+__udivsi3 = 0x4000c7c8;
+__umoddi3 = 0x4000d280;
+__umodsi3 = 0x4000c7d0;
+__umulsidi3 = 0x4000c7d8;
+__unorddf2 = 0x400637f4;
+__unordsf2 = 0x40063478;