Refactored to maintain a separate cloud version

Moves 12 packages from internal/ to pkg/ (config, id, validate, events, db,
auth, lifecycle, scheduler, channels, audit, service) so they can be imported
by the enterprise repo as a Go module dependency.

Introduces pkg/cpextension (shared Extension interface + ServerContext) and
pkg/cpserver (Run() entrypoint with functional options) so the enterprise
main.go can call cpserver.Run(cpserver.WithExtensions(...)) without duplicating
the 20-step server bootstrap. Adds db/migrations/embed.go for go:embed access
to OSS SQL migrations from the enterprise module.

cmd/control-plane/main.go is reduced to a 10-line wrapper around cpserver.Run.

internal/hostagent/server.go

@@ -80,6 +80,7 @@ func (s *Server) CreateSandbox(
 		SandboxId: sb.ID,
 		Status:    string(sb.Status),
 		HostIp:    sb.HostIP.String(),
+		Metadata:  sb.Metadata,
 	}), nil
 }
 
@@ -108,7 +109,7 @@ func (s *Server) ResumeSandbox(
 	req *connect.Request[pb.ResumeSandboxRequest],
 ) (*connect.Response[pb.ResumeSandboxResponse], error) {
 	msg := req.Msg
-	sb, err := s.mgr.Resume(ctx, msg.SandboxId, int(msg.TimeoutSec))
+	sb, err := s.mgr.Resume(ctx, msg.SandboxId, int(msg.TimeoutSec), msg.KernelVersion)
 	if err != nil {
 		return nil, connect.NewError(connect.CodeInternal, err)
 	}
@@ -124,6 +125,7 @@ func (s *Server) ResumeSandbox(
 		SandboxId: sb.ID,
 		Status:    string(sb.Status),
 		HostIp:    sb.HostIP.String(),
+		Metadata:  sb.Metadata,
 	}), nil
 }
 
@@ -564,6 +566,7 @@ func (s *Server) ListSandboxes(
 			CreatedAtUnix:    sb.CreatedAt.Unix(),
 			LastActiveAtUnix: sb.LastActiveAt.Unix(),
 			TimeoutSec:       int32(sb.TimeoutSec),
+			Metadata:         sb.Metadata,
 		}
 	}