ditch arduino's hacky-hacky FS, back to zephyr native

mg24 fix
dfu zip generation fix

zephcore/boards/example_board/board.conf

@@ -105,11 +105,11 @@ CONFIG_BT_DIS_MODEL_NUMBER_STR="My Board v1"
 # CRITICAL: SoftDevice version determines the app start address!
 # Check your board's Arduino platformio.ini for which linker script it uses:
 #   nrf52840_s140_v6*.ld → s140 v6.1.1, app@0x26000, FWID=0x00B6
-#   nrf52840_s140_v7*.ld → s140 v7.3.0, app@0x27000, FWID=0x0100
+#   nrf52840_s140_v7*.ld → s140 v7.3.0, app@0x27000, FWID=0x0123
 # Your board.overlay partition table MUST match (see Section 4 in board.overlay).
 # Wrong address = bootloop / bricked device with no USB/BLE/logs.
 # CONFIG_ZEPHCORE_SD_FWID=0x00B6     # SoftDevice firmware ID (s140 v6.1.1)
-# CONFIG_ZEPHCORE_SD_FWID=0x0100     # SoftDevice firmware ID (s140 v7.3.0)
+# CONFIG_ZEPHCORE_SD_FWID=0x0123     # SoftDevice firmware ID (s140 v7.3.0)
 #
 # --- MG24 (Silicon Labs) ---
 # Requires: west blobs fetch hal_silabs (before first build)

zephcore/boards/example_board/board.overlay

@@ -82,6 +82,13 @@
 		 */
 
 		/* --- Display (uncomment if board has OLED/LCD/e-paper) ---
+		 * Setting zephyr,display auto-enables CONFIG_DISPLAY,
+		 * CONFIG_CHARACTER_FRAMEBUFFER, and the UI page system.
+		 * No board.conf changes needed.
+		 * HEAP: 128x64 OLEDs fit in the default 2KB heap.
+		 *       Larger displays need CONFIG_HEAP_MEM_POOL_SIZE
+		 *       override in board.conf (e.g. 6144 for 200x200 EPD).
+		 *
 		 * zephyr,display = &oled;       I2C OLED (SH1106, SSD1306)
 		 * zephyr,display = &epd;        SPI e-paper (SSD1681, etc.)
 		 */