feat: Docker-Support (Compose + Dockerfiles)

- docker-compose.yml: db (timescaledb/pg17) + backend + frontend
- backend/Dockerfile: multi-stage (golang:1.24-alpine -> debian:bookworm-slim)
- frontend/Dockerfile: multi-stage (node:22-alpine -> nginx:alpine), Build-Args fuer VITE_*
- frontend/nginx.conf: SPA-Routing + Asset-Caching
- .env.example: BACKEND_HOST, DB_PASSWORD, JWT_SECRET, API_KEY
- backend/config/config.go: ENV-Var-Support vervollstaendigt (JWT_SECRET, API_KEY, DB_PORT, DB_USER, DB_NAME)
- backend/config.yaml.example: ENV-Var Kommentare ergaenzt
- README: Docker-Quickstart als empfohlener Einstieg (3 Befehle)
- .gitignore: .env zur ignore-Liste hinzugefuegt

backend/config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/cynfo/rmm-backend/db"
@@ -41,7 +42,7 @@ func Load(path string) (*Config, error) {
 		return nil, err
 	}
 
-	// Env overrides
+	// Env overrides — alle Werte koennen via ENV ueberschrieben werden (z.B. Docker)
 	if v := os.Getenv("RMM_LISTEN_ADDR"); v != "" {
 		cfg.ListenAddr = v
 	}
@@ -51,12 +52,32 @@ func Load(path string) (*Config, error) {
 	if v := os.Getenv("RMM_TLS_KEY"); v != "" {
 		cfg.TLSKey = v
 	}
+	if v := os.Getenv("RMM_JWT_SECRET"); v != "" {
+		cfg.JWTSecret = v
+	}
+	if v := os.Getenv("RMM_API_KEY"); v != "" {
+		cfg.APIKeys = append(cfg.APIKeys, v)
+	}
 	if v := os.Getenv("RMM_DB_HOST"); v != "" {
 		cfg.Database.Host = v
 	}
+	if v := os.Getenv("RMM_DB_PORT"); v != "" {
+		if port := 0; len(v) > 0 {
+			fmt.Sscanf(v, "%d", &port)
+			if port > 0 {
+				cfg.Database.Port = port
+			}
+		}
+	}
+	if v := os.Getenv("RMM_DB_USER"); v != "" {
+		cfg.Database.User = v
+	}
 	if v := os.Getenv("RMM_DB_PASSWORD"); v != "" {
 		cfg.Database.Password = v
 	}
+	if v := os.Getenv("RMM_DB_NAME"); v != "" {
+		cfg.Database.DBName = v
+	}
 
 	return cfg, nil
 }