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/riscv/asserts.x

@@ -0,0 +1,42 @@
+
+
+/* Do not exceed this mark in the error messages above                                    | */
+ASSERT(ORIGIN(ROTEXT) % 4 == 0, "
+ERROR(riscv-rt): the start of the ROTEXT must be 4-byte aligned");
+
+ASSERT(ORIGIN(RODATA) % 4 == 0, "
+ERROR(riscv-rt): the start of the RODATA must be 4-byte aligned");
+
+ASSERT(ORIGIN(REGION_DATA) % 4 == 0, "
+ERROR(riscv-rt): the start of the REGION_DATA must be 4-byte aligned");
+
+ASSERT(ORIGIN(ROTEXT) % 4 == 0, "
+ERROR(riscv-rt): the start of the ROTEXT must be 4-byte aligned");
+
+ASSERT(ORIGIN(REGION_STACK) % 4 == 0, "
+ERROR(riscv-rt): the start of the REGION_STACK must be 4-byte aligned");
+
+ASSERT(_stext % 4 == 0, "
+ERROR(riscv-rt): `_stext` must be 4-byte aligned");
+
+ASSERT(_data_start % 4 == 0 && _data_end % 4 == 0, "
+BUG(riscv-rt): .data is not 4-byte aligned");
+
+ASSERT(_sidata % 4 == 0, "
+BUG(riscv-rt): the LMA of .data is not 4-byte aligned");
+
+ASSERT(_bss_start % 4 == 0 && _bss_end % 4 == 0, "
+BUG(riscv-rt): .bss is not 4-byte aligned");
+
+ASSERT(_stext + SIZEOF(.text) < ORIGIN(ROTEXT) + LENGTH(ROTEXT), "
+ERROR(riscv-rt): The .text section must be placed inside the ROTEXT region.
+Set _stext to an address smaller than 'ORIGIN(ROTEXT) + LENGTH(ROTEXT)'");
+
+ASSERT(SIZEOF(.got) == 0, "
+.got section detected in the input files. Dynamic relocations are not
+supported. If you are linking to C code compiled using the `gcc` crate
+then modify your build script to compile the C code _without_ the
+-fPIC flag. See the documentation of the `gcc::Config.fpic` method for
+details.");
+
+/* Do not exceed this mark in the error messages above                                    | */