feat: initial tools service with document scanner, image & PDF tools

Self-hosted document scanner and media processing tools.
- Rust Axum gateway + worker pool with NATS JetStream
- Next.js 16 frontend with shadcn/ui
- Scanner pipeline: edge detection, warp, binarization, OCR
- Image tools: compress, resize, convert
- PDF tools: merge, split, compress
- CI/CD with Docker multi-stage build

Co-Authored-By: Kilo <kilo@kilo.ai>

frontend/src/app/health/route.ts

@@ -0,0 +1,18 @@
+import { NextResponse } from "next/server";
+
+const RUST_GATEWAY = process.env.RUST_GATEWAY_URL || "http://localhost:3001";
+
+export async function GET() {
+  try {
+    const response = await fetch(`${RUST_GATEWAY}/health`, {
+      signal: AbortSignal.timeout(5000),
+    });
+    const data = await response.json();
+    return NextResponse.json(data);
+  } catch {
+    return NextResponse.json(
+      { status: "error", message: "Gateway unreachable" },
+      { status: 503 },
+    );
+  }
+}