WP-00: project skeleton with three-level test harness

Cargo workspace (domain, application, infrastructure, api), axum health endpoint
with SPA fallback, Vue 3 + Tailwind frontend, Vitest, Playwright, Makefile,
Gitea Actions CI and README.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,33 @@
+.PHONY: dev dev-backend dev-frontend build test test-backend test-frontend test-ui lint fmt
+
+dev: ## run backend + frontend dev servers
+	@$(MAKE) -j2 dev-backend dev-frontend
+
+dev-backend:
+	cd backend && cargo run -p api
+
+dev-frontend:
+	cd frontend && npm run dev
+
+build: ## production build: frontend into frontend/dist, backend release binary
+	cd frontend && npm ci && npm run build
+	cd backend && cargo build --release -p api
+
+test: test-backend test-frontend test-ui
+
+test-backend:
+	cd backend && cargo test --workspace
+
+test-frontend:
+	cd frontend && npm test
+
+test-ui:
+	cd frontend && npm run test:ui
+
+lint:
+	cd backend && cargo fmt --check && cargo clippy --workspace --all-targets -- -D warnings
+	cd frontend && npm run lint && npm run typecheck
+
+fmt:
+	cd backend && cargo fmt
+	cd frontend && npm run format