feat(infra): add tools service with document scanner, image & PDF tools

Implement self-hosted document scanner and media processing tools as
an alternative to CamScanner/ilovepdf without third-party uploads.

Backend: Rust Axum gateway + worker pool with NATS JetStream queue
Frontend: Next.js 16 + shadcn/ui + Tailwind v4 + Framer Motion
Pipeline: Canny edge detection -> DLT homography warp -> Sauvola
binarization -> Hough deskew -> Tesseract OCR -> searchable PDF

Phase 1 (MVP) delivers:
- Document scanner with perspective correction and OCR
- Image compress/resize/convert tools
- PDF merge/split/compress tools
- Real-time WebSocket progress updates
- Rate limiting, auto-cleanup, Prometheus metrics
- Full CI/CD pipeline with Docker multi-stage build

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

apps/tools/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