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>

backend/crates/api/src/test_support.rs

@@ -0,0 +1,18 @@
+//! Helpers to build a fully wired app on an in-memory database for integration tests.
+use crate::{build_app, AppState, Config};
+use axum::Router;
+
+pub fn test_config() -> Config {
+    Config {
+        database_url: "sqlite::memory:".into(),
+        jwt_secret: "test-secret-test-secret-test-secret-1234".into(),
+        bind: "127.0.0.1:0".parse().unwrap(),
+        bootstrap_admin: None,
+        cookie_secure: false,
+        frontend_dir: "/nonexistent".into(),
+    }
+}
+
+pub async fn build_test_app() -> Router {
+    build_app(AppState { cfg: test_config() })
+}