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>

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: ["**"]
+  pull_request:
+    branches: ["**"]
+
+jobs:
+  build-and-test:
+    name: Build and Test
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: "1.22"
+
+      - name: Verify dependencies
+        working-directory: src
+        run: go mod verify
+
+      - name: Vet
+        working-directory: src
+        run: go vet ./...
+
+      - name: Test
+        working-directory: src
+        run: go test -v -race ./...
+
+      - name: Build all binaries
+        working-directory: src
+        run: |
+          mkdir -p ../bin
+          go build -o ../bin/keycape             ./cmd/keycape/
+          go build -o ../bin/validator           ./cmd/validator/
+          go build -o ../bin/lldap-export        ./cmd/lldap-export/
+          go build -o ../bin/keycape-to-keycloak ./cmd/keycape-to-keycloak/
+          go build -o ../bin/lldap-to-ldap       ./cmd/lldap-to-ldap/