Phase 4: Dioxus frontend with dataset browser and SQL query editor

- ui: Dioxus WASM app with dataset sidebar, SQL editor (Ctrl+Enter), results table
- ui: dynamic API base URL (same-origin for nginx, port-based for local dev)
- gateway: CORS enabled for cross-origin requests
- nginx: lakehouse.devop.live proxies UI (:3300) + API (:3100) on same origin
- justfile: ui-build, ui-serve, sidecar, up commands added

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

justfile

@@ -15,6 +15,28 @@ test:
 run:
     cargo run --bin gateway
 
+# Build UI (WASM)
+ui-build:
+    cd crates/ui && dx build --platform web
+
+# Serve UI (dev)
+ui-serve:
+    cd target/dx/ui/debug/web/public && python3 -m http.server 3300 --bind 0.0.0.0
+
+# Start sidecar
+sidecar:
+    cd sidecar && uvicorn sidecar.main:app --host 0.0.0.0 --port 3200
+
+# Start everything (gateway + sidecar + UI)
+up:
+    @echo "Starting gateway on :3100..."
+    @cargo run --bin gateway &
+    @echo "Starting sidecar on :3200..."
+    @cd sidecar && uvicorn sidecar.main:app --host 0.0.0.0 --port 3200 &
+    @echo "Starting UI on :3300..."
+    @cd target/dx/ui/debug/web/public && python3 -m http.server 3300 --bind 0.0.0.0 &
+    @echo "All services started."
+
 # Check without building
 check:
     cargo check --workspace