feat: builder + App runner, Makefile (v1.1.0)

Builder (cli.For[C]): Root/Dir/Cmd/SlotDir/Slot construct the tree
without repeating the [C] type parameter at every node; returns plain
*Node[C] so it interoperates with struct-literal construction.

App[C]: collapses the per-binary main.go — standard flags
(-color/-json/-version, -server when configured), mode-aware color
defaults, version banner, client connect, and the one-shot-vs-shell
split — into one Main(). Transport-agnostic via a Connect callback, so
it never assumes gRPC.

Makefile: `make check` = fixstyle vet lint test (the pre-commit gate),
plus build and a linux+openbsd cross target. The example now dogfoods
both Builder and App. Tests cover the builder tree and App's one-shot
dispatch / -version / nil-Connect paths.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Makefile

@@ -0,0 +1,33 @@
+# SPDX-FileCopyrightText: (C) Copyright 2026 Pim van Pelt <pim@ipng.ch>
+# SPDX-License-Identifier: Apache-2.0
+
+.PHONY: help all check test fixstyle vet lint build cross
+
+help: ## Show this help
+	@printf "Usage: make <target>\n\nTargets:\n"
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | \
+		awk 'BEGIN {FS = ":.*?## "}; {printf "  \033[36m%-12s\033[0m %s\n", $$1, $$2}'
+
+all: check ## Alias for check
+
+check: fixstyle vet lint test ## Run the full pre-commit gate (format, vet, lint, test)
+
+test: ## Run all Go unit tests
+	go test ./...
+
+fixstyle: ## Format the Go tree (gofmt)
+	gofmt -w .
+
+vet: ## Run go vet across the tree
+	go vet ./...
+
+lint: ## Run golangci-lint across the Go tree
+	golangci-lint run ./...
+
+build: ## Build all packages for the host platform
+	go build ./...
+
+cross: ## Verify the tree builds on Linux and OpenBSD
+	GOOS=linux   GOARCH=amd64 go build ./...
+	GOOS=linux   GOARCH=arm64 go build ./...
+	GOOS=openbsd GOARCH=amd64 go build ./...