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/Dockerfile

@@ -0,0 +1,31 @@
+FROM golang:1.24-alpine AS builder
+
+WORKDIR /build
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o rmm-backend .
+
+# ---
+
+FROM debian:bookworm-slim
+
+RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+COPY --from=builder /build/rmm-backend .
+COPY config.yaml.example config.yaml.example
+
+RUN mkdir -p certs
+
+EXPOSE 8443
+
+# Umgebungsvariablen mit Standardwerten (koennen alle per ENV ueberschrieben werden)
+ENV RMM_LISTEN_ADDR=":8443" \
+    RMM_DB_HOST="db" \
+    RMM_DB_PORT="5432" \
+    RMM_DB_USER="rmm" \
+    RMM_DB_NAME="rmm"
+
+CMD ["./rmm-backend"]