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>

.gitignore

@@ -0,0 +1,17 @@
+# Rust
+backend/target/
+
+# Node
+frontend/node_modules/
+frontend/.next/
+frontend/out/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo