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/config/config.go

@@ -3,15 +3,17 @@ package config
 import (
 	"os"
 
+	"github.com/cynfo/rmm-backend/db"
+
 	"gopkg.in/yaml.v3"
 )
 
 type Config struct {
-	ListenAddr string   `yaml:"listen_addr"`
-	TLSCert    string   `yaml:"tls_cert"`
-	TLSKey     string   `yaml:"tls_key"`
-	APIKeys    []string `yaml:"api_keys"`
-	DBPath     string   `yaml:"db_path"`
+	ListenAddr string    `yaml:"listen_addr"`
+	TLSCert    string    `yaml:"tls_cert"`
+	TLSKey     string    `yaml:"tls_key"`
+	APIKeys    []string  `yaml:"api_keys"`
+	Database   db.DBConfig `yaml:"database"`
 }
 
 func Load(path string) (*Config, error) {
@@ -19,7 +21,14 @@ func Load(path string) (*Config, error) {
 		ListenAddr: ":8443",
 		TLSCert:    "certs/server.crt",
 		TLSKey:     "certs/server.key",
-		DBPath:     "rmm.db",
+		Database: db.DBConfig{
+			Host:     "127.0.0.1",
+			Port:     5432,
+			User:     "rmm",
+			Password: "",
+			DBName:   "rmm",
+			SSLMode:  "disable",
+		},
 	}
 
 	data, err := os.ReadFile(path)
@@ -41,8 +50,11 @@ func Load(path string) (*Config, error) {
 	if v := os.Getenv("RMM_TLS_KEY"); v != "" {
 		cfg.TLSKey = v
 	}
-	if v := os.Getenv("RMM_DB_PATH"); v != "" {
-		cfg.DBPath = v
+	if v := os.Getenv("RMM_DB_HOST"); v != "" {
+		cfg.Database.Host = v
+	}
+	if v := os.Getenv("RMM_DB_PASSWORD"); v != "" {
+		cfg.Database.Password = v
 	}
 
 	return cfg, nil