[CONTRACTS] Deploy contract to Stellar testnet

[DavisVT]

Deploy the Bounty contract to Stellar testnet and document the contract address and deployment steps.

[liangtovi-debug]

/attempt #4

Plan:

1. Build and optimize the bounty Soroban contract WASM from this repo.
2. Configure Stellar testnet identity/network and deploy the contract.
3. Capture the deployed contract address and invocation checks.
4. Document exact deployment steps + commands in repo docs and open a PR with test/build evidence.

[liangtovi-debug]

/claim

Implemented in PR: #12

What changed:

• Built and deployed the Soroban bounty contract to Stellar testnet.
• Documented full deployment steps, contract ID, and transaction links in README.

Deployment result:

• Contract ID: CDST3TZ2XMOKTKUWIZNVOFKBKSHEDAPCFRXFQTKU6COK6FICIUTO6COD
• WASM upload tx: 057144fc5bd581bb296abe4170dd1fd2c96d81368c222d5daba4fb2e1074cdc0
• Deploy tx: 2734e045e7081d9277ab3ee2fba5d57a1bfb6318eb36785896234e0c3667182e

Validation:

• cd contracts/bounty && cargo test
• cd contracts/bounty && stellar contract build