added more file type specific instructions

I hope that coding results will be better and more consistent

docker/Dockerfile.backend.dev

@@ -5,6 +5,20 @@ FROM golang:1.25-alpine
 # Install necessary packages for CGO and SQLite
 RUN apk add --no-cache gcc musl-dev sqlite-dev
 
+# Install Chromium for PDF rendering
+RUN apk add --no-cache \
+    chromium \
+    chromium-chromedriver \
+    nss \
+    freetype \
+    harfbuzz \
+    ca-certificates \
+    ttf-freefont
+
+# Set Chrome path for chromedp
+ENV CHROME_BIN=/usr/bin/chromium-browser \
+    CHROME_PATH=/usr/bin/chromium-browser
+
 # Install Air für Live-Reloading (kompatible Version für Go 1.23)
 #RUN go install github.com/cosmtrek/air@v1.49.0
 RUN go install github.com/air-verse/air@latest