feat: Add Rust API Server with REST and GraphQL support

- Implement JWT authentication layer
- Add Engine Registry with 20+ conversion engines
- Implement Conversion Service with background job processing
- REST API endpoints for file conversion operations
- GraphQL API with queries and mutations
- Comprehensive error handling with conversion suggestions
- Integration tests for both REST and GraphQL APIs
- Complete API documentation

Features:
- REST API: /api/v1/* endpoints
- GraphQL API: /graphql endpoint with playground
- JWT Bearer token authentication
- Engine validation with alternative suggestions
- File download via API (not exposing file paths)
- Support for FFmpeg, ImageMagick, LibreOffice, Pandoc, and more

api-server/Cargo.toml

@@ -0,0 +1,63 @@
+[package]
+name = "convertx-api"
+version = "0.1.0"
+edition = "2021"
+authors = ["ConvertX Team"]
+description = "ConvertX API Server - REST & GraphQL file conversion API"
+license = "MIT"
+repository = "https://github.com/your-username/ConvertX-CN"
+
+[dependencies]
+# Web framework
+axum = { version = "0.7", features = ["multipart"] }
+tokio = { version = "1.0", features = ["full"] }
+tower = "0.4"
+tower-http = { version = "0.5", features = ["cors", "trace", "fs"] }
+
+# GraphQL
+async-graphql = { version = "7.0", features = ["uuid"] }
+async-graphql-axum = "7.0"
+
+# Authentication
+jsonwebtoken = "9.0"
+
+# Serialization
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+
+# Async utilities
+futures = "0.3"
+async-trait = "0.1"
+
+# UUID for job IDs
+uuid = { version = "1.0", features = ["v4", "serde"] }
+
+# File handling
+mime_guess = "2.0"
+tempfile = "3.0"
+
+# Logging
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
+# Error handling
+thiserror = "1.0"
+anyhow = "1.0"
+
+# Time
+chrono = { version = "0.4", features = ["serde"] }
+
+# Base64 encoding
+base64 = "0.22"
+
+# Configuration
+dotenvy = "0.15"
+
+# Process execution (for calling converters)
+tokio-process = "0.2"
+
+[dev-dependencies]
+axum-test = "14.0"
+tokio-test = "0.4"
+reqwest = { version = "0.11", features = ["json", "multipart"] }
+pretty_assertions = "1.0"