feat: implement T01-T04 — Go module, canonical model, LDAP validator, error taxonomy

- T01: Go module (keycape), full directory skeleton, Makefile, CI workflow
- T02: spec/canonical-model.yaml with 6 entities + Go domain types
- T03: spec/ldap-schema.yaml + validator binary with structural/semantic rules
- T04: Error taxonomy — 4 stable error types, JSON format, HTTP helpers

28 tests pass, go vet clean, go build clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Makefile

@@ -0,0 +1,29 @@
+GOBIN ?= $(shell go env GOPATH)/bin
+BINDIR = ../bin
+
+.PHONY: all build test lint vet clean
+
+all: vet lint test build
+
+build:
+	go build -o $(BINDIR)/keycape            ./cmd/keycape/
+	go build -o $(BINDIR)/validator          ./cmd/validator/
+	go build -o $(BINDIR)/lldap-export       ./cmd/lldap-export/
+	go build -o $(BINDIR)/keycape-to-keycloak ./cmd/keycape-to-keycloak/
+	go build -o $(BINDIR)/lldap-to-ldap      ./cmd/lldap-to-ldap/
+
+test:
+	go test ./...
+
+vet:
+	go vet ./...
+
+lint:
+	@if command -v golangci-lint >/dev/null 2>&1; then \
+		golangci-lint run ./...; \
+	else \
+		echo "golangci-lint not installed, skipping (run: go install github.com/golangci/golangci-lint/cmd/golangci-lint@latest)"; \
+	fi
+
+clean:
+	rm -rf $(BINDIR)