feat: add configurable JWT secret, anonymous authentication and standardize rust practices

[vihu]

Hello!

Firstly, thank you for starting this project and secondly I apologize for the large diff here.

Basically the changes in this branch are to bring the project upto some sort of production-ready standardization along with an introduction of anonymous mode for potentially hosting the server somewhere. That said, below is the full rundown of the most critical changes.

Summary

• Add JWT authentication with configurable secrets via environment variables
• Introduce optional anonymous authentication mode for clients to generate their own tokens
• Add CLI improvements via clap and workspace dependency consolidation

Changes

Authentication (conflux/src/auth.rs)

• Add JWT_SECRET static via LazyLock loading from CONFLUX_JWT_SECRET env var
• Panic in release mode if CONFLUX_JWT_SECRET is not set; use dev default in debug mode
• Add validate_token_anonymous() function that validates JWT structure without signature verification
• Add 12 unit tests covering validation, expiry, future-dated tokens, wrong secrets, and signature bypass

Server (conflux/src/server.rs)

• Add anonymous_mode: bool field to AppState
• Route token validation conditionally based on mode

CLI (confluxd/src/main.rs)

• Migrate to clap with derive macros
• Add --port, --host, --anonymous, --idle-timeout arguments

Infrastructure

• Consolidate dependencies to workspace level
• Add rust-toolchain.toml and .github/workflows/rust.yml

Usage

# Production (requires CONFLUX_JWT_SECRET)
CONFLUX_JWT_SECRET=your-secret-here cargo run -p confluxd

# Anonymous mode (clients can self-sign tokens)
cargo run -p confluxd -- --anonymous

Breaking Changes

Production deployments must set CONFLUX_JWT_SECRET: Release builds will panic on startup if the environment variable is not set.