Update boot order configuration for eMMC first, then network

Modify the first-boot script and documentation to set the EEPROM boot order to 0xf21, prioritizing eMMC boot followed by network boot. Adjust network boot settings for faster failure on DHCP timeouts and update related scripts and documentation to reflect these changes. Enhance the rescue script to directly modify EEPROM settings without requiring a chroot into eMMC, streamlining the recovery process for devices stuck in network-only boot. Update relevant documentation to ensure clarity on the new boot order and its implications.

emmc-provisioning/docs/NETWORK-BOOT-LXC.md

@@ -67,7 +67,7 @@ Your current LXC already has eth0 (10.130.60.141) and eth1 (10.20.50.1); the set
 
 ## After setup: reTerminal network boot
 
-1. Set the reTerminal **boot order** to try network first (e.g. `BOOT_ORDER=0x21`; see cloud-init/first-boot).
+1. Set the reTerminal **boot order** to try eMMC first, then network (e.g. `BOOT_ORDER=0xf21`; see cloud-init/first-boot).
 2. Connect the reTerminal to the **same network as the LXC’s eth1** (e.g. 10.20.50.0/24).
 3. Power on; it will get an IP via DHCP and load boot files via TFTP from the LXC.
 4. For **provisioning** (Backup/Deploy), the netboot environment must run **network-client/provisioning-client.sh** with `PROVISIONING_SERVER=http://10.20.50.1:5000` so it talks to the dashboard on the LXC.
@@ -102,7 +102,7 @@ Each line is: *expiry_epoch MAC IP hostname client_id*. Example: `1734567890 aa:
 ## Testing network boot
 
 1. **Prerequisites**
-   - reTerminal has **BOOT_ORDER=0x21** (network first). Check on the device:  
+   - reTerminal has **BOOT_ORDER=0xf21** (eMMC first, then network). Check on the device:  
      `ssh pi@<device-ip> 'bash -s' < emmc-provisioning/scripts/check-network-boot-priority.sh`
    - LXC network-boot options are **enabled**: on the LXC run  
      `/opt/cm4-provisioning/toggle-network-boot-dhcp.sh status` → should print `enabled`. If not: `toggle-network-boot-dhcp.sh enable`