Pass LVM config to Instance on construction

[guifranchi]

Summary

• Instance::new() initialises its lvm field with empty strings and has a with_lvm() builder method intended to populate it from ManagerConfig
• with_lvm() was never called at the construction site in slot.rs
• As a result, lvcreate was invoked with an empty volume group, producing paths like /base-default instead of runners/base-default, causing every slot boot cycle to fail with:

  "/rootfs-default-0": Invalid path for Logical Volume.
  Volume group name  has invalid characters
  lvcreate snapshot failed: /base-default -> rootfs-default-0
  

Fix

Chain .with_lvm(&config.lvm) onto the Instance::new() call in run_slot().

Test plan

• Build and release a new version
• Deploy to ci-hel3 (staging manager node) and verify boot cycles succeed in journalctl -u actions-runner