feat: upgrade to Go 1.25.3 and update build to include api-gateway

- Create ADR-0034 documenting Go version upgrade to 1.25.3
- Mark ADR-0002 as superseded by ADR-0034
- Update CI workflow to use Go 1.25.3
- Update Makefile to build both platform and api-gateway binaries
- Update CI workflow to build and upload both binaries
- Update documentation (ADR README and mkdocs.yml) to include ADR-0034

Makefile

@@ -18,7 +18,7 @@ help:
 	@echo "  make lint          - Run linters"
 	@echo "  make fmt           - Format code"
 	@echo "  make fmt-check     - Check code formatting"
-	@echo "  make build         - Build platform binary"
+	@echo "  make build         - Build platform and api-gateway binaries"
 	@echo "  make clean         - Clean build artifacts"
 	@echo "  make docker-build  - Build Docker image"
 	@echo "  make docker-run    - Run Docker container"
@@ -85,9 +85,10 @@ fmt-check:
 	@echo "Code is properly formatted"
 
 build:
-	@echo "Building platform binary..."
-	$(GO) build -v -o $(BINARY_PATH) ./cmd/platform
-	@echo "Build complete: $(BINARY_PATH)"
+	@echo "Building platform and api-gateway binaries..."
+	$(GO) build -v -o bin/platform ./cmd/platform
+	$(GO) build -v -o bin/api-gateway ./cmd/api-gateway
+	@echo "Build complete: bin/platform, bin/api-gateway"
 
 clean:
 	@echo "Cleaning build artifacts..."