[infra] Complete deploy-contract.sh with initialize and program bootstrap

[yinkscss]

Context

scripts/deploy-contract.sh builds WASM and echoes example Soroban CLI commands but does not perform deploy or initialize calls.

Problem

Maintainers lack a repeatable script to deploy the escrow contract and capture ESCROW_CONTRACT_ID for gateway configuration.

Proposed scope

• Extend script to deploy WASM via Soroban CLI when credentials are present
• Call initialize(admin, gateway, token) after deploy
• Print contract ID and suggested .env exports
• Guard with env vars (DEPLOYER_SECRET, TOKEN_CONTRACT_ID, GATEWAY_PUBLIC) and clear error messages when missing

Acceptance criteria

• Script deploys to testnet when Soroban CLI and secrets are configured
• Script invokes initialize with admin, gateway, and token addresses
• Script outputs ESCROW_CONTRACT_ID for gateway env
• README or docs/core-loop.md references the script in testnet walkthrough

References

• scripts/deploy-contract.sh
• contracts/waveflow-escrow/src/contract.rs (initialize)
• .env.example
• docs/core-loop.md