feat: initial etrelay UDP relay with master heartbeat

Makefile

@@ -0,0 +1,59 @@
+ROOT_DIR := $(dir $(realpath $(lastword $(MAKEFILE_LIST))))
+
+NAME := etrelay
+VERSION := $(shell grep -m1 '^version' Cargo.toml | cut -d '"' -f2)
+GNU := x86_64-unknown-linux-gnu
+MUSL := x86_64-unknown-linux-musl
+
+# Release artifacts: <name>-v<version>-<target triple> (+ .sha256).
+DIST_DIR := $(ROOT_DIR)dist
+DYNAMIC_BIN := $(DIST_DIR)/$(NAME)-v$(VERSION)-$(GNU)
+STATIC_BIN := $(DIST_DIR)/$(NAME)-v$(VERSION)-$(MUSL)
+
+.PHONY: show lint format check build static release diagrams clean
+
+show:
+	@echo "$(NAME) version: $(VERSION)"
+
+lint:
+	cargo clippy --fix --allow-dirty
+
+format:
+	cargo fmt --all
+
+check: lint format
+
+# Dynamic (glibc): runs on hosts with the same or newer glibc.
+build: check
+	cargo build --release --target $(GNU)
+	@$(call dist,$(GNU),$(DYNAMIC_BIN))
+
+# Static (musl): runs on any x86_64 Linux. Pure Rust, no musl-gcc needed.
+static: check
+	rustup target add $(MUSL)
+	cargo build --release --target $(MUSL)
+	@$(call dist,$(MUSL),$(STATIC_BIN))
+
+release: build static
+
+# PlantUML sources (diagrams/*.puml) -> PNG next to them, used by ENGINE.md.
+diagrams:
+	plantuml -tpng $(ROOT_DIR)diagrams/*.puml
+	@ls -1 $(ROOT_DIR)diagrams/*.png
+
+clean:
+	cargo clean
+	rm -rf $(DIST_DIR)
+
+# $(call dist,<target triple>,<artifact path>): copy the release binary to dist/ + checksum.
+define dist
+mkdir -p $(DIST_DIR)
+cp $(ROOT_DIR)target/$(1)/release/$(NAME) $(2)
+cd $(DIST_DIR) && sha256sum $(notdir $(2)) > $(notdir $(2)).sha256
+ls -lh $(2)
+endef
+
+# Deployment targets (deploy, logs, status...) kept with the infra config, reached through
+# the local .deploy symlink (gitignored). Optional: silently skipped when absent.
+ETRELAY_DIR := $(patsubst %/,%,$(ROOT_DIR))
+-include $(ROOT_DIR).deploy/Makefile