feat: add provider and user CLI tools

[Wilbert957]

Background

The billing proxy currently lacks CLI tooling for provider setup and user interactions. All on-chain operations require manual scripting.

Provider CLI (cmd/provider)

provider init-service \
  --rpc <url> --chain-id <id> --contract <addr> \
  --key <provider-private-key> \
  --tee-signer <tee-eth-address> \
  --url <service-url> \
  --price <neuron-per-sec> \
  --create-fee <neuron>

• Calls addOrUpdateService with provider ≠ TEE signer (real TEE deployment)
• Optional: withdraw, service-status

User CLI (cmd/user)

user deposit    --rpc ... --contract ... --key ... --provider <addr> --amount <0G>
user acknowledge --rpc ... --contract ... --key ... --provider <addr>
user balance    --rpc ... --contract ... --address ... --provider <addr>
user create     --api <billing-proxy-url> --key ...
user list       --api <billing-proxy-url> --key ...
user stop       --api <billing-proxy-url> --key ... --id <sandbox-id>

Provider Deployment Flow

1. tapp-cli start-app — deploy billing proxy to TEE server
2. provider init-service — register service on-chain (provider key + TEE signer address)
3. Share API URL + contract address with users

Notes

• Contract can be 0G official canonical deployment (shared) or provider-deployed
• cmd/setup remains as dev/test-only single-account tool
• User sandbox operations require EIP-191 signed requests to billing proxy

[Wilbert957]

Implemented: cmd/provider and cmd/user CLIs are complete with register, status, withdraw, snapshot management, deposit, acknowledge, balance, create, list, start, stop, delete, exec, ssh-access, toolbox commands.