feat: Enable multi-arch Docker image builds (#137)

The Docker images published to GHCR only supported the linux/amd64
architecture, preventing native execution on arm64 systems like
Apple Silicon Macs.

This updates the GitHub Actions workflow to build and push images
for both linux/amd64 and linux/arm64 platforms.

Closes #136

Author: ShivaGupta-14

.github/workflows/docker.yml

@@ -31,6 +31,7 @@ jobs:
         with:
           context: ./frontend
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: |
             ghcr.io/ccextractor/frontend:latest
             ghcr.io/ccextractor/frontend:${{ github.sha }}
@@ -66,6 +67,7 @@ jobs:
         with:
           context: ./backend
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: |
             ghcr.io/ccextractor/backend:latest
             ghcr.io/ccextractor/backend:${{ github.sha }}