refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

internal/apps/agent/heartbeat/service.go

@@ -0,0 +1,33 @@
+package heartbeat
+
+import (
+	"context"
+
+	"github.com/Rain-kl/Wavelet/internal/apps/agent/protocol"
+)
+
+type Client interface {
+	RegisterNode(ctx context.Context, payload protocol.NodePayload) (*protocol.RegisterNodeResponse, error)
+	Heartbeat(ctx context.Context, payload protocol.NodePayload) (*protocol.HeartbeatResult, error)
+	SetToken(token string)
+}
+
+type Service struct {
+	client Client
+}
+
+func New(client Client) *Service {
+	return &Service{client: client}
+}
+
+func (s *Service) Register(ctx context.Context, payload protocol.NodePayload) (*protocol.RegisterNodeResponse, error) {
+	return s.client.RegisterNode(ctx, payload)
+}
+
+func (s *Service) Heartbeat(ctx context.Context, payload protocol.NodePayload) (*protocol.HeartbeatResult, error) {
+	return s.client.Heartbeat(ctx, payload)
+}
+
+func (s *Service) SetToken(token string) {
+	s.client.SetToken(token)
+}