feat(observability): phase 3 - direct proxy creation with validation

Add standalone proxy management:
- Multi-step validation pipeline (DNS, TCP, HTTP) with diagnostic hints
- Proxy lifecycle: create/update/delete via NPM API with SSL auto-assign
- Periodic health monitoring (5min) with event log on status transitions
- Unified /api/proxies/all endpoint merging standalone + managed proxies
- Frontend types and API functions for downstream UI phases

cmd/server/main.go

@@ -24,6 +24,7 @@ import (
 	"github.com/alexei/docker-watcher/internal/logging"
 	"github.com/alexei/docker-watcher/internal/notify"
 	"github.com/alexei/docker-watcher/internal/npm"
+	"github.com/alexei/docker-watcher/internal/proxy"
 	"github.com/alexei/docker-watcher/internal/registry"
 	"github.com/alexei/docker-watcher/internal/stale"
 	"github.com/alexei/docker-watcher/internal/store"
@@ -137,9 +138,17 @@ func main() {
 		slog.Warn("failed to start stale scanner", "error", err)
 	}
 
+	// Initialize proxy manager and health monitor.
+	proxyManager := proxy.NewManager(db, npmClient)
+	proxyHealth := proxy.NewHealthMonitor(db, eventBus)
+	if err := proxyHealth.Start("5m"); err != nil {
+		slog.Warn("failed to start proxy health monitor", "error", err)
+	}
+
 	// Build API server.
 	apiServer := api.NewServer(db, dockerClient, npmClient, dep, webhookHandler, eventBus, encKey)
 	apiServer.SetStaleScanner(staleScanner)
+	apiServer.SetProxyManager(proxyManager)
 	router := apiServer.Router()
 
 	// Serve embedded static files for the SPA frontend.
@@ -181,6 +190,7 @@ func main() {
 	slog.Info("shutting down...")
 
 	// Stop accepting new work.
+	proxyHealth.Stop()
 	staleScanner.Stop()
 	poller.Stop()