Pass LVM config to Instance on construction

Instance::new() initialises lvm with empty strings and relies on
with_lvm() being called afterwards to populate it from ManagerConfig,
but with_lvm() was never called. As a result, lvcreate was invoked
with an empty volume group, producing paths like "/base-default"
instead of "runners/base-default", causing all slot boot cycles to fail.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: guifranchi

manager/src/slot.rs

@@ -22,7 +22,8 @@ pub fn run_slot(config: Arc<ManagerConfig>, role: &Role, idx: usize) -> Result<(
         &config.run_path,
         role,
         idx as u8,
-    );
+    )
+    .with_lvm(&config.lvm);
 
     instance.setup().map_err(|e| {
         error!(role = %role.name, idx, error = %e, "slot setup failed");