rfs(firmware): pack full Alpine linux-firmware set from container and overmount /lib/firmware

Change pack source: install all linux-firmware* packages in container and pack from /lib/firmware via [bash.rfs_common_install_all_alpine_firmware_packages()](scripts/rfs/common.sh:290) used by [bash.pack-firmware.sh](scripts/rfs/pack-firmware.sh:21). At runtime, overmount firmware flist on /lib/firmware by updating [sh.firmware.sh](config/zinit/init/firmware.sh:10). Update docs to reflect /lib/firmware mount and new pack strategy.

scripts/rfs/pack-firmware.sh

@@ -1,10 +1,8 @@
 #!/bin/bash
 # Pack firmware tree into an RFS flist and patch manifest stores for Garage web endpoint.
 # - Computes FULL_KERNEL_VERSION from configs (not strictly needed for firmware, but kept uniform)
-# - Selects firmware directory with priority:
-#     1) $PROJECT_ROOT/firmware
-#     2) $PROJECT_ROOT/initramfs/lib/firmware
-#     3) /lib/firmware
+# - Installs all Alpine linux-firmware* packages into the build container (/lib/firmware)
+# - Packs from container's /lib/firmware into an RFS flist (reproducible, full set)
 # - Manifest name: firmware-<FIRMWARE_TAG or YYYYMMDD>.fl
 # - Uploads blobs to S3 (Garage) via rfs store URI
 # - Patches .fl sqlite stores table to use WEB_ENDPOINT for read-only fetches
@@ -25,8 +23,10 @@ rfs_common_load_rfs_s3_config
 rfs_common_build_s3_store_uri
 rfs_common_locate_rfs
 
-section "Locating firmware directory"
-rfs_common_locate_firmware_dir
+section "Installing full Alpine firmware set in container (source: /lib/firmware)"
+rfs_common_install_all_alpine_firmware_packages
+export FIRMWARE_DIR="/lib/firmware"
+log_info "Using firmware source dir: ${FIRMWARE_DIR}"
 
 TAG="$(rfs_common_firmware_tag)"
 MANIFEST_NAME="firmware-${TAG}.fl"