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/main.rs

@@ -0,0 +1,15 @@
+use api::{build_app, AppState, Config};
+use tracing_subscriber::EnvFilter;
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let _ = dotenvy::dotenv();
+    tracing_subscriber::fmt()
+        .with_env_filter(EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()))
+        .init();
+    let cfg = Config::from_env()?;
+    let listener = tokio::net::TcpListener::bind(cfg.bind).await?;
+    tracing::info!("listening on http://{}", cfg.bind);
+    axum::serve(listener, build_app(AppState { cfg })).await?;
+    Ok(())
+}