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/common/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "tools-common"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+serde.workspace = true
+serde_json.workspace = true
+uuid.workspace = true
+chrono.workspace = true
+thiserror.workspace = true
+tracing.workspace = true
+async-nats.workspace = true
+redis.workspace = true