feat(uavcan): flash firmware onto CAN nodes from SD card (#27043)

Place firmware .bin files at the SD card root or staging directory
(/fs/microsd/ufw_staging/); on boot the UAVCAN server migrates them
to /fs/microsd/ufw/ and updates FW.db, then flashes any connected
node whose firmware version mismatches.

- Add firmware migration from SD root and staging dir into /fs/microsd/ufw/
- Maintain FW.db flat-file database mapping board IDs to original filenames
- Use cache-aligned DMA-safe read/write buffers (required on STM32H7)
- Add Tools/auterion/remote_update_fmu.sh for SSH-based FMU+canio updates

ROMFS/px4fmu_common/init.d/rcS

@@ -150,6 +150,14 @@ fi
 
 if [ $USE_ALT_UPDATE_DIRS = yes ]
 then
+	# Check for new CAN-firmware directory
+	if [ -e /fs/microsd/ufw_staging_tmp ]
+	then
+		echo "Updating CAN firmware staging directory"
+		rm -r /fs/microsd/ufw_staging
+		mv /fs/microsd/ufw_staging_tmp /fs/microsd/ufw_staging
+	fi
+
 	# Check for an update of the ext_autostart folder, and replace the old one with it
 	if [ -e /fs/microsd/ext_autostart_new ]
 	then