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>

bible-local/architecture/runtime-flows.md

@@ -109,6 +109,7 @@ Build host notes:
 - `bee-gpu-burn` worker must be built against cached CUDA userspace headers from `build-cublas.sh`, not against random host-installed CUDA headers.
 - The live ISO must ship `libcublas`, `libcublasLt`, and `libcudart` together with `libcuda` so tensor-core stress works without internet or package installs at boot.
 - The source overlay in `iso/overlay/` is treated as immutable source. Build-time files are injected only into the staged overlay.
+- ISO filename, squashfs filename, ISO volume label, and the live system's hostname all derive from the same `easy-bee-<variant>-v<version>` scheme (`ISO_BASENAME`/`SQUASHFS_FILENAME`/`BEE_ISO_VOLUME`/`BEE_HOSTNAME` in `build.sh`) instead of the live-build default (`debian`). Keep new naming derived from `PROJECT_VERSION_EFFECTIVE`/`BUILD_VARIANT` in sync with this set rather than hardcoding a new scheme.
 - The live-build workdir under `dist/` is disposable; source files under `iso/builder/` stay clean.
 - Container build requires `--privileged` because `live-build` uses mounts/chroots/loop devices during ISO assembly.
 - On macOS / Docker Desktop, the builder still must run as `linux/amd64` so the shipped ISO binaries remain `amd64`.