feat: complete deploy-contract.sh with initialize and program bootstrap (Closes #4)

[ZacLou]

Closes #4

Changes

Completes scripts/deploy-contract.sh from a placeholder echo script into a full deployment pipeline:

4-step pipeline

1. Build WASM — cargo build --release -p waveflow-escrow --target wasm32-unknown-unknown
2. Deploy contract — soroban contract deploy with configurable RPC, network, and passphrase
3. Initialize contract — soroban contract invoke -- initialize with admin, gateway, and token addresses
4. Bootstrap program (optional) — create_program when GITHUB_REPO is set

Environment variables

Variable	Required	Description
DEPLOYER_SECRET	Yes	Soroban identity secret key
ADMIN_ADDRESS	Yes (for init)	Contract admin Stellar address
GATEWAY_ADDRESS	Yes (for init)	Gateway oracle address
TOKEN_ADDRESS	Yes (for init)	Payout token contract ID
GITHUB_REPO	No	Optional repo slug for program bootstrap
SOROBAN_NETWORK	No	Default: testnet
SOROBAN_RPC_URL	No	Default: Soroban testnet RPC

Post-deployment summary

Prints contract ID, addresses, and actionable next steps (set env vars, fund contract, start gateway).