Phase 0: bootstrap Rust workspace

- Cargo workspace with 6 crates: shared, storaged, catalogd, queryd, aibridge, gateway
- shared: types (DatasetId, ObjectRef, SchemaFingerprint, DatasetManifest) + error enum
- gateway: Axum HTTP entrypoint with nested service routers + tracing
- All services expose /health stubs
- justfile with build/test/run recipes
- PRD, phase tracker, and ADR docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/gateway/src/main.rs

@@ -0,0 +1,29 @@
+use axum::{Router, routing::get};
+use tower_http::trace::TraceLayer;
+use tracing_subscriber::{EnvFilter, fmt, layer::SubscriberExt, util::SubscriberInitExt};
+
+#[tokio::main]
+async fn main() {
+    tracing_subscriber::registry()
+        .with(EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info")))
+        .with(fmt::layer())
+        .init();
+
+    let app = Router::new()
+        .route("/health", get(health))
+        .nest("/storage", storaged::service::router())
+        .nest("/catalog", catalogd::service::router())
+        .nest("/query", queryd::service::router())
+        .nest("/ai", aibridge::service::router())
+        .layer(TraceLayer::new_for_http());
+
+    let addr = "0.0.0.0:3100";
+    tracing::info!("gateway listening on {addr}");
+
+    let listener = tokio::net::TcpListener::bind(addr).await.unwrap();
+    axum::serve(listener, app).await.unwrap();
+}
+
+async fn health() -> &'static str {
+    "lakehouse ok"
+}