feat: Hub monitoring takeover — event push system + config cleanup (v0.21.0)

Replace external Healthchecks.io with Hub-native event system. Controller
now pushes structured events via POST /api/v1/event with typed detail
structs. Hub handles dead man's switch, notification dispatch, and cooldowns.

Phase 5: PushEvent() core method, 21 event types, expanded notification
settings (11 toggles), Hub connection monitoring on dashboard, alerts.
Phase 6: Deprecation log for ping UUIDs, pinger kept for transition.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/report/pusher.go

@@ -8,11 +8,20 @@ import (
 	"log"
 	"net/http"
 	"strings"
+	"sync"
 	"time"
 
 	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
 )
 
+// PushStatus tracks the last hub push attempt and result.
+type PushStatus struct {
+	LastAttempt time.Time
+	LastSuccess time.Time
+	LastError   string
+	Consecutive int // consecutive failures
+}
+
 // Pusher sends reports to the central hub.
 type Pusher struct {
 	hubURL     string
@@ -20,6 +29,9 @@ type Pusher struct {
 	httpClient *http.Client
 	logger     *log.Logger
 	enabled    bool
+
+	statusMu sync.RWMutex
+	status   PushStatus
 }
 
 // NewPusher creates a new report pusher from hub configuration.
@@ -48,6 +60,10 @@ func (p *Pusher) Push(report *Report) error {
 
 	url := p.hubURL + "/api/v1/report"
 
+	p.statusMu.Lock()
+	p.status.LastAttempt = time.Now()
+	p.statusMu.Unlock()
+
 	var lastErr error
 	for attempt := 0; attempt < 3; attempt++ {
 		if attempt > 0 {
@@ -74,14 +90,31 @@ func (p *Pusher) Push(report *Report) error {
 
 		if resp.StatusCode >= 200 && resp.StatusCode < 300 {
 			p.logger.Printf("[INFO] Hub report pushed successfully (%d bytes)", len(data))
+			p.statusMu.Lock()
+			p.status.LastSuccess = time.Now()
+			p.status.LastError = ""
+			p.status.Consecutive = 0
+			p.statusMu.Unlock()
 			return nil
 		}
 		lastErr = fmt.Errorf("HTTP %d", resp.StatusCode)
 	}
 
+	p.statusMu.Lock()
+	p.status.LastError = lastErr.Error()
+	p.status.Consecutive++
+	p.statusMu.Unlock()
+
 	return fmt.Errorf("hub push failed after 3 attempts: %w", lastErr)
 }
 
+// GetStatus returns a snapshot of the current push status.
+func (p *Pusher) GetStatus() PushStatus {
+	p.statusMu.RLock()
+	defer p.statusMu.RUnlock()
+	return p.status
+}
+
 // PushInfraBackup sends the infrastructure backup payload to the Hub.
 // Uses the same retry logic as Push.
 func (p *Pusher) PushInfraBackup(data []byte) error {