feat: add multi-architecture Docker build setup

- Add Docker BuildKit builder setup for AMD64 and ARM64 platforms
- Update backend and frontend Dockerfiles with platform flags
- Create comprehensive build scripts for multi-arch workflows
- Add verification script to test multi-architecture images
- Update Makefile with multi-arch Docker targets
- Add detailed documentation for multi-architecture setup

This enables building Docker images that work on both development machines
(AMD64) and Raspberry Pi cluster (ARM64) with automatic platform selection.

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Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

scripts/build-multiarch.sh

@@ -0,0 +1,87 @@
+#!/bin/bash
+
+# Multi-architecture Docker build script for Adopt-a-Street
+# Builds and pushes images for AMD64 and ARM64 platforms
+
+set -e
+
+# Configuration
+REGISTRY="gitea-http.taildb3494.ts.net:3000/will/adopt-a-street"
+BACKEND_IMAGE="${REGISTRY}/backend"
+FRONTEND_IMAGE="${REGISTRY}/frontend"
+VERSION=${1:-latest}
+
+# Colors for output
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+BLUE='\033[0;34m'
+NC='\033[0m' # No Color
+
+echo -e "${BLUE}🏗️  Adopt-a-Street Multi-Architecture Docker Build${NC}"
+echo -e "${BLUE}===============================================${NC}"
+echo ""
+
+# Check if we're logged into the registry
+echo -e "${YELLOW}🔐 Checking registry authentication...${NC}"
+if ! docker info | grep -q "Username"; then
+    echo -e "${RED}❌ Not logged into Docker registry. Please run: docker login ${REGISTRY}${NC}"
+    exit 1
+fi
+
+# Setup multi-architecture builder
+echo -e "${YELLOW}🔧 Setting up multi-architecture builder...${NC}"
+./scripts/setup-multiarch-builder.sh
+
+# Function to build and push image
+build_image() {
+    local service_name=$1
+    local dockerfile_path=$2
+    local build_context=$3
+    local image_tag=$4
+    
+    echo -e "${YELLOW}📦 Building ${service_name} image for AMD64 and ARM64...${NC}"
+    
+    # Build and push multi-architecture image
+    docker buildx build \
+        --platform linux/amd64,linux/arm64 \
+        --file "${dockerfile_path}" \
+        --tag "${image_tag}:${VERSION}" \
+        --tag "${image_tag}:latest" \
+        --push \
+        "${build_context}"
+    
+    echo -e "${GREEN}✅ ${service_name} image built and pushed successfully!${NC}"
+    echo ""
+}
+
+# Build backend
+echo -e "${BLUE}🔙 Building Backend Image${NC}"
+build_image "Backend" "backend/Dockerfile" "backend" "${BACKEND_IMAGE}"
+
+# Build frontend
+echo -e "${BLUE}🎨 Building Frontend Image${NC}"
+build_image "Frontend" "frontend/Dockerfile" "frontend" "${FRONTEND_IMAGE}"
+
+# Verify images
+echo -e "${YELLOW}🔍 Verifying multi-architecture images...${NC}"
+echo -e "${BLUE}Backend image manifest:${NC}"
+docker buildx imagetools inspect "${BACKEND_IMAGE}:${VERSION}"
+echo ""
+echo -e "${BLUE}Frontend image manifest:${NC}"
+docker buildx imagetools inspect "${FRONTEND_IMAGE}:${VERSION}"
+
+echo -e "${GREEN}🎉 Multi-architecture build completed successfully!${NC}"
+echo ""
+echo -e "${BLUE}Images pushed:${NC}"
+echo "  - ${BACKEND_IMAGE}:${VERSION}"
+echo "  - ${FRONTEND_IMAGE}:${VERSION}"
+echo ""
+echo -e "${BLUE}To pull on different architectures:${NC}"
+echo "  # AMD64 (x86_64)"
+echo "  docker pull ${BACKEND_IMAGE}:${VERSION}"
+echo "  docker pull ${FRONTEND_IMAGE}:${VERSION}"
+echo ""
+echo "  # ARM64 (Raspberry Pi)"
+echo "  docker pull ${BACKEND_IMAGE}:${VERSION}"
+echo "  docker pull ${FRONTEND_IMAGE}:${VERSION}"