iso: give the live image a real hostname instead of live-build's default "debian"

Adds BEE_HOSTNAME, derived with the same easy-bee-<variant>-v<version>
scheme already used for ISO_BASENAME/SQUASHFS_FILENAME/BEE_ISO_VOLUME, and
wires it into auto/config via lb config --hostname. Documented the shared
naming scheme as a runtime-flows.md invariant.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

iso/builder/auto/config

@@ -22,6 +22,8 @@ else
     LB_ISO_VOLUME="EASY_BEE_${BEE_GPU_VENDOR_UPPER:-NVIDIA}"
 fi
 
+LB_HOSTNAME="${BEE_HOSTNAME:-easy-bee}"
+
 lb config noauto \
     --distribution bookworm \
     --architectures amd64 \
@@ -36,6 +38,7 @@ lb config noauto \
     --linux-flavours "amd64" \
     --linux-packages "${LB_LINUX_PACKAGES}" \
     --memtest memtest86+ \
+    --hostname "${LB_HOSTNAME}" \
     --iso-volume "${LB_ISO_VOLUME}" \
     --iso-application "EASY-BEE-${BEE_GPU_VENDOR_UPPER:-NVIDIA}" \
     --bootappend-live "boot=live live-media=/dev/disk/by-label/${LB_ISO_VOLUME} live-media-label=${LB_ISO_VOLUME} components video=1920x1080 console=ttyS0,115200n8 console=tty0 loglevel=3 systemd.show_status=1 username=bee user-fullname=Bee modprobe.blacklist=nouveau,snd_hda_intel,snd_hda_codec_realtek,snd_hda_codec_generic,soundcore" \