Add support for RockBase NM-CYD-C5 (ESP32-C5, ST7789 320x240)

[Copilot]

Adds a new hardware model for the RockBase NM-CYD-C5 "Cheap Yellow Display" board: ESP32-C5 (RISC-V, Wi-Fi 6 + BLE 5), 2.8" ST7789 SPI color LCD (320x240), 16MB flash / 8MB PSRAM.

Kconfig

• New DRAFTLING_MODEL_NM_CYD_C5 choice (depends on IDF_TARGET_ESP32C5)
• New DRAFTLING_DISPLAY_ST7789 derived flag gating the new backend; wired into DRAFTLING_DISPLAY_COLOR, DRAFTLING_DISPLAY_HAS_BACKLIGHT, DRAFTLING_WAKEUP_GPIO, width/height

Display backend

• New components/display/display_st7789.cpp using the upstream espressif/esp_lcd_st7789 managed component (esp_lcd_new_panel_st7789()), unlike the hand-rolled AXS15231B vendor sequence
• No local framebuffer -- pushes RGB565 tiles directly via esp_lcd_panel_draw_bitmap()
• LEDC PWM backlight, sleep/wake/deep-sleep-prepare hooks
• New display_st7789_config_t struct-based init (mirrors the display_axs15231b_config_t pattern) since the panel needs more pins than the generic display_init() slots

display_st7789_config_t cfg = {};
cfg.spi_host = LCD_SPI_HOST;
cfg.cs = LCD_CS_PIN; cfg.dc = LCD_DC_PIN; cfg.rst = LCD_RST_PIN; cfg.bl = LCD_BL_PIN;
cfg.width = DISPLAY_WIDTH; cfg.height = DISPLAY_HEIGHT;
cfg.invert_colors = true; // IPS panel
display_st7789_init(&cfg);

Board wiring

• New main/boards/nm_cyd_c5.h: display, MicroSD, and (unused) XPT2046 touch CS all share one physical SPI bus with separate CS lines. No battery monitor, no wake GPIO (no user buttons besides power) -- deep sleep wakes only via hardware RESET, matching M5Stack Tab5 precedent
• main/main.cpp: new display-init branch; SD-init reuses the display's already-initialized SPI bus (mosi/miso/sck = -1)

Build config

• sdkconfig.defaults.esp32c5: Quad-mode PSRAM (C5 silicon has no Octal support), BLE-only Bluedroid, WiFi tuning
• sdkconfig.defaults.nm_cyd_c5: target + model selection
• New nm_cyd_c5 preset in CMakePresets.json

Docs

• README.md / AGENTS.md: added board entry, updated preset list and board counts

Known limitation

XPT2046 resistive touch is not wired up -- Draftling's touchscreen component currently only supports I2C capacitive controllers. The pin is reserved in the board header for future work; the board remains keyboard-driven like every other supported board.

• Fixes add support for NMTech NM-CYD-C5 #31