feat(setup): rewrite setup.sh — full one-click AL2023+Ubuntu enclave+register+service

Replaces the broken Ubuntu-only setup.sh with a comprehensive script that:
- Detects AL2023 (dnf) vs Ubuntu (apt) automatically
- Applies all AL2023 Nitro fixes (CPU pool rc=-22, /run/nitro_enclaves perms,
  vhost_vsock vs vmw_vsock_virtio_transport, fix-nitro-pool.service)
- Downloads pre-built EIF from release; falls back to building from binary
- Starts enclave in production mode (no --debug-console)
- Creates socat vsock bridge as systemd service
- Installs vram-validator + vram-cli binaries
- Downloads .env.example, prompts for wallet mnemonic interactively
- Runs vram-cli register-validator + register-enclave automatically
- Writes UID and enclave pubkey back to ~/.env
- Creates and starts vram-validator.service

Usage: curl -fsSL https://raw.githubusercontent.com/VRAM-AI/vram-validator/main/setup.sh | sudo bash

Author: User