fix(heartbeat): resolve bug where service could never start

HeartbeatService.Start() always returned early because running()
checked stopChan closure state, which is "open" (= true) for a
newly created service. This caused Start() to interpret a fresh
service as "already running" and skip launching the goroutine.

Introduce a `started` bool field to separate "has been started"
from "has not been stopped", fixing both the start failure and
a potential double-close panic on Stop().

pkg/heartbeat/service.go

@@ -14,6 +14,7 @@ type HeartbeatService struct {
 	interval    time.Duration
 	enabled     bool
 	mu          sync.RWMutex
+	started     bool
 	stopChan    chan struct{}
 }
 
@@ -31,7 +32,7 @@ func (hs *HeartbeatService) Start() error {
 	hs.mu.Lock()
 	defer hs.mu.Unlock()
 
-	if hs.running() {
+	if hs.started {
 		return nil
 	}
 
@@ -39,6 +40,7 @@ func (hs *HeartbeatService) Start() error {
 		return fmt.Errorf("heartbeat service is disabled")
 	}
 
+	hs.started = true
 	go hs.runLoop()
 
 	return nil
@@ -48,10 +50,11 @@ func (hs *HeartbeatService) Stop() {
 	hs.mu.Lock()
 	defer hs.mu.Unlock()
 
-	if !hs.running() {
+	if !hs.started {
 		return
 	}
 
+	hs.started = false
 	close(hs.stopChan)
 }