Containerd socket path defaults diverge between server.go and containerd component

Issue

The default containerd socket path is defined in two places with different values:

1. server.go:177 sets default to: /var/lib/miren/containerd/containerd.sock (flat)
2. containerd/containerd.go:64 would default to: /var/lib/miren/containerd/run/containerd.sock (with run/ subdir)

In practice, server.go's default wins because it sets the socket path before passing to the component, so the component's default never applies. This creates confusing divergent defaults.

Expected Behavior

Both places should agree on the same default path structure.

Suggested Fix

Pick one approach and make both consistent:

• Option A: Use flat structure /var/lib/miren/containerd/containerd.sock in both places (matches current behavior)
• Option B: Use run/ subdirectory in both places (more traditional Unix structure)

Code Locations

• cli/commands/server.go:177
• components/containerd/containerd.go:62-64

Impact

Low - current behavior works correctly, but the code is confusing for developers.