SQLite durch PostgreSQL + TimescaleDB ersetzt

- Backend DB komplett auf PostgreSQL 17 + TimescaleDB 2.25.1 umgestellt
- pgx pure-Go Driver (kein CGO), modernc/sqlite entfernt
- Hypertable 'metrics' fuer Time-Series Daten
- Automatische Metrik-Extraktion bei jedem Heartbeat:
  CPU, RAM, Uptime, Disk, Network-Traffic, Gateway RTT/Loss
- Retention Policy: 90 Tage, Compression nach 7 Tagen
- Neue API-Endpoints: GET /metrics (raw) + GET /metrics/summary (aggregiert)
- time_bucket() Aggregation (5min, 1h, etc.)
- config.yaml: database-Block statt db_path
- docs/POSTGRES_SETUP.md: Installationsanleitung
- README aktualisiert

backend/api/metrics.go

@@ -0,0 +1,83 @@
+package api
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+)
+
+// GET /api/v1/agents/{id}/metrics — Metriken abfragen
+func (h *Handler) getMetrics() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		agentID := r.PathValue("id")
+		metric := r.URL.Query().Get("metric")
+
+		// Zeitraum (default: letzte 24h)
+		from := time.Now().Add(-24 * time.Hour)
+		to := time.Now()
+
+		if f := r.URL.Query().Get("from"); f != "" {
+			if t, err := time.Parse(time.RFC3339, f); err == nil {
+				from = t
+			}
+		}
+		if t := r.URL.Query().Get("to"); t != "" {
+			if parsed, err := time.Parse(time.RFC3339, t); err == nil {
+				to = parsed
+			}
+		}
+
+		limit := 1000
+		if l := r.URL.Query().Get("limit"); l != "" {
+			if parsed, err := strconv.Atoi(l); err == nil && parsed > 0 {
+				limit = parsed
+			}
+		}
+
+		results, err := h.db.GetMetrics(agentID, metric, from, to, limit)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "Metriken laden fehlgeschlagen")
+			return
+		}
+		writeJSON(w, http.StatusOK, results)
+	}
+}
+
+// GET /api/v1/agents/{id}/metrics/summary — Aggregierte Metriken (Durchschnitt/Min/Max)
+func (h *Handler) getMetricsSummary() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		agentID := r.PathValue("id")
+		metric := r.URL.Query().Get("metric")
+
+		if metric == "" {
+			writeError(w, http.StatusBadRequest, "Parameter 'metric' erforderlich")
+			return
+		}
+
+		bucket := r.URL.Query().Get("bucket")
+		if bucket == "" {
+			bucket = "5 minutes"
+		}
+
+		from := time.Now().Add(-24 * time.Hour)
+		to := time.Now()
+
+		if f := r.URL.Query().Get("from"); f != "" {
+			if t, err := time.Parse(time.RFC3339, f); err == nil {
+				from = t
+			}
+		}
+		if t := r.URL.Query().Get("to"); t != "" {
+			if parsed, err := time.Parse(time.RFC3339, t); err == nil {
+				to = parsed
+			}
+		}
+
+		results, err := h.db.GetMetricsSummary(agentID, metric, bucket, from, to)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "Metriken laden fehlgeschlagen")
+			return
+		}
+		writeJSON(w, http.StatusOK, results)
+	}
+}

backend/api/tunnel_proxy.go

@@ -26,6 +26,10 @@ func (h *Handler) setupTunnelRoutes(mux *http.ServeMux, hub *ws.Hub) {
 	mux.HandleFunc("PUT /api/v1/agents/{id}/proxy/{tunnel_id}/", h.httpProxy(hub))
 	mux.HandleFunc("DELETE /api/v1/agents/{id}/proxy/{tunnel_id}/", h.httpProxy(hub))
 	
+	// Metrics-Endpoints
+	mux.HandleFunc("GET /api/v1/agents/{id}/metrics", h.getMetrics())
+	mux.HandleFunc("GET /api/v1/agents/{id}/metrics/summary", h.getMetricsSummary())
+
 	// WireGuard-Endpoints
 	mux.HandleFunc("POST /api/v1/agents/{id}/wireguard/peers", h.wgAddPeer(hub))
 	mux.HandleFunc("GET /api/v1/agents/{id}/wireguard/peers", h.wgListPeers(hub))