host api alignment (#7)

* feat: add Firecracker API client methods for VM pause/resume and snapshots

Add PatchVm, GetVm, PutSnapshotCreate, and PutSnapshotLoad methods to the
API client, along with supporting types (VmState, SnapshotCreateParams,
SnapshotLoadParams, MemBackend).

* feat: add snapshot data layer - contract types, model, store, config

Add SnapshotID and snapshot contract types, SnapshotRecord model,
store interface CRUD methods with file store implementation,
snapshot paths helper, SnapshotsDir config, and directory creation.

* feat: add runtime methods for VM pause, resume, snapshot, and restore

Implement Pause, Resume, CreateSnapshot, and RestoreBoot on the
firecracker Runtime. RestoreBoot launches a jailer, stages snapshot
files into the chroot, loads the snapshot, and resumes the VM.

* feat: add daemon snapshot create, restore, and reconciliation logic

Implement CreateSnapshot (pause, snapshot, COW-copy disk, resume),
RestoreSnapshot (COW-copy disk, RestoreBoot, wait for guest),
GetSnapshot, ListSnapshots, DeleteSnapshotByID, and crash recovery
reconciliation for snapshot and restore operations.

* feat: add HTTP endpoints for snapshot create, get, list, delete, restore

Wire 5 snapshot routes: POST /machines/{id}/snapshots (create),
GET /machines/{id}/snapshots (list), GET /snapshots/{id} (get),
DELETE /snapshots/{id} (delete), POST /snapshots/{id}/restore (restore).

* fix: cross-device rename, restore network, and snapshot cleanup

- Replace os.Rename with copy+remove for moving snapshot files out of
  /proc/<pid>/root/ (cross-device link error on Linux)
- Reconfigure network interface after snapshot load so the restored VM
  uses its own tap device instead of the source VM's
- Clean partial snapshot dirs immediately on failure instead of only
  via reconcile
- Reject snapshot requests while a machine operation is already pending

* fix: test and modify snapshot runtime

* feat: snapshot lifecycle update, align runtime issues between host image
and daemon

internal/firecracker/api.go

@@ -146,6 +146,69 @@ func (c *apiClient) PutVsock(ctx context.Context, spec VsockSpec) error {
 	return c.do(ctx, http.MethodPut, "/vsock", body, nil, http.StatusNoContent)
 }
 
+type VmState string
+
+const (
+	VmStatePaused  VmState = "Paused"
+	VmStateResumed VmState = "Resumed"
+)
+
+type vmRequest struct {
+	State VmState `json:"state"`
+}
+
+type vmResponse struct {
+	State string `json:"state"`
+}
+
+type SnapshotCreateParams struct {
+	MemFilePath  string `json:"mem_file_path"`
+	SnapshotPath string `json:"snapshot_path"`
+	SnapshotType string `json:"snapshot_type"`
+}
+
+type SnapshotLoadParams struct {
+	SnapshotPath     string            `json:"snapshot_path"`
+	MemBackend       *MemBackend       `json:"mem_backend,omitempty"`
+	ResumeVm         bool              `json:"resume_vm"`
+	NetworkOverrides []NetworkOverride `json:"network_overrides,omitempty"`
+	VsockOverride    *VsockOverride    `json:"vsock_override,omitempty"`
+}
+
+type MemBackend struct {
+	BackendType string `json:"backend_type"`
+	BackendPath string `json:"backend_path"`
+}
+
+type NetworkOverride struct {
+	IfaceID     string `json:"iface_id"`
+	HostDevName string `json:"host_dev_name"`
+}
+
+type VsockOverride struct {
+	UDSPath string `json:"uds_path"`
+}
+
+func (c *apiClient) PatchVm(ctx context.Context, state VmState) error {
+	return c.do(ctx, http.MethodPatch, "/vm", vmRequest{State: state}, nil, http.StatusNoContent)
+}
+
+func (c *apiClient) GetVm(ctx context.Context) (*vmResponse, error) {
+	var response vmResponse
+	if err := c.do(ctx, http.MethodGet, "/vm", nil, &response, http.StatusOK); err != nil {
+		return nil, err
+	}
+	return &response, nil
+}
+
+func (c *apiClient) PutSnapshotCreate(ctx context.Context, params SnapshotCreateParams) error {
+	return c.do(ctx, http.MethodPut, "/snapshot/create", params, nil, http.StatusNoContent)
+}
+
+func (c *apiClient) PutSnapshotLoad(ctx context.Context, params SnapshotLoadParams) error {
+	return c.do(ctx, http.MethodPut, "/snapshot/load", params, nil, http.StatusNoContent)
+}
+
 func (c *apiClient) do(ctx context.Context, method string, endpoint string, input any, output any, wantStatus int) error {
 	var body io.Reader
 	if input != nil {