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>

backend/gateway/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "tools-gateway"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+tools-common = { path = "../common" }
+
+axum = { version = "0.8", features = ["multipart", "ws"] }
+tower = "0.5"
+tower-http = { version = "0.6", features = ["cors", "trace", "limit"] }
+tokio.workspace = true
+tokio-util = { version = "0.7", features = ["io"] }
+serde.workspace = true
+serde_json.workspace = true
+uuid.workspace = true
+chrono.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+async-nats.workspace = true
+redis.workspace = true
+thiserror.workspace = true
+anyhow.workspace = true
+futures = "0.3"