feat(ci): add format check, PR validation, and Docker buildx

- Add cargo fmt --check to enforce code formatting
- Add pull_request trigger for PR validation
- Split workflow into parallel jobs (format, clippy, build, docker)
- Integrate Docker Buildx with DinD service
- Add BuildKit caching for faster builds
- Add local test script (scripts/test-ci-locally.sh)
- Add comprehensive documentation

All local CI checks pass ✅

scripts/test-ci-locally.sh

@@ -0,0 +1,100 @@
+#!/bin/bash
+
+# Local CI Validation Script
+# Tests all CI checks locally before pushing
+
+set -e
+
+echo "=========================================="
+echo "Local CI Validation"
+echo "=========================================="
+echo ""
+
+cd "$(git rev-parse --show-toplevel)/backend"
+
+# Test 1: Format check
+echo "🔍 Test 1: Code Formatting Check"
+echo "Command: cargo fmt --all -- --check"
+if cargo fmt --all -- --check; then
+    echo "✅ PASS - Code is properly formatted"
+else
+    echo "❌ FAIL - Code needs formatting"
+    echo "Run: cargo fmt --all"
+    exit 1
+fi
+echo ""
+
+# Test 2: Clippy
+echo "🔍 Test 2: Clippy Lint"
+echo "Command: cargo clippy --all-targets --all-features -- -D warnings"
+if cargo clippy --all-targets --all-features -- -D warnings; then
+    echo "✅ PASS - No clippy warnings"
+else
+    echo "❌ FAIL - Clippy found issues"
+    exit 1
+fi
+echo ""
+
+# Test 3: Build
+echo "🔍 Test 3: Build Release Binary"
+echo "Command: cargo build --release"
+if cargo build --release; then
+    echo "✅ PASS - Build successful"
+    BINARY_SIZE=$(du -h target/release/normogen-backend | cut -f1)
+    echo "Binary size: $BINARY_SIZE"
+else
+    echo "❌ FAIL - Build failed"
+    exit 1
+fi
+echo ""
+
+# Test 4: Verify binary exists
+echo "🔍 Test 4: Verify Binary"
+if [ -f target/release/normogen-backend ]; then
+    echo "✅ PASS - Binary exists"
+    file target/release/normogen-backend
+else
+    echo "❌ FAIL - Binary not found"
+    exit 1
+fi
+echo ""
+
+# Test 5: Docker build (only if Docker is available locally)
+if command -v docker &> /dev/null && docker info &> /dev/null; then
+    echo "🔍 Test 5: Docker Build"
+    echo "Command: docker build -f docker/Dockerfile -t normogen-backend:test ."
+    if docker build -f docker/Dockerfile -t normogen-backend:test .; then
+        echo "✅ PASS - Docker image built"
+        docker images normogen-backend:test
+    else
+        echo "❌ FAIL - Docker build failed"
+        exit 1
+    fi
+    echo ""
+else
+    echo "⚠️  SKIP - Docker not available locally"
+    echo "   Note: Docker build will run in Forgejo CI on Solaria"
+    echo "   This is expected and OK!"
+    echo ""
+fi
+
+echo "=========================================="
+echo "✅ All Local CI Checks Passed!"
+echo "=========================================="
+echo ""
+echo "Changes ready to commit:"
+echo "  ✅ Code formatting"
+echo "  ✅ Clippy linting"
+echo "  ✅ Build successful"
+echo "  ✅ Binary created"
+echo ""
+echo "Next steps:"
+echo "  1. Commit the changes"
+echo "  2. Push to Forgejo"
+echo "  3. Watch CI run at: http://gitea.solivarez.com.ar/alvaro/normogen/actions"
+echo ""
+echo "The Forgejo CI will also:"
+echo "  • Verify formatting (same as local)"
+echo "  • Run Clippy (same as local)"
+echo "  • Build the binary (same as local)"
+echo "  • Build Docker image with Buildx (runs on Solaria)"