feat: add automated deploy script for testnet and mainnet

[collinsezedike]

Summary

• Adds scripts/deploy.sh, which builds a contract, deploys it to testnet, mainnet, or futurenet via stellar-cli, and optionally calls its initialize function
• Each deployment is appended (never overwritten) to deployments/<network>.jsonl, keyed by contract, wasm hash, source account, and timestamp, so history survives redeploys
• Init args can be passed via --init-args, a --init-args-file, or a default file at scripts/init-args/<contract>.args (documented in scripts/init-args/README.md)
• --dry-run prints the planned build, deploy, and initialize commands without executing anything, useful for verifying init args before a real mainnet deploy
• Network RPC URL and passphrase are set per network (testnet, futurenet, mainnet) and can be overridden with --rpc-url / --passphrase

Closes #636

Test plan

• bash -n scripts/deploy.sh (syntax check)
• Verified --help, missing/invalid --contract, invalid --network, and the missing-init-args warning path
• Ran --dry-run against a real contract (price-oracle) and confirmed the planned build/deploy/invoke commands are correct
• Cross-checked all stellar CLI flags (--source, --rpc-url, --network-passphrase, --id) against stellar contract deploy --help / stellar contract invoke --help on stellar-cli 27.0.0

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