feat: add testnet deploy and init script for escrow contract

[Dayz-tech-co]

Closes #485

---

#539
This PR adds a secure, reviewable testnet deployment flow for the escrow/commitment core contract under the new contracts/ workspace scaffold.

What changed
Added contracts/scripts/deploy-testnet.sh

Builds from contracts/Cargo.toml using stellar contract build
Deploys the compiled WASM to Stellar testnet
Invokes initialize(admin, token, fee_recipient)
Upserts the deployed contract id into:
NEXT_PUBLIC_COMMITMENT_CORE_CONTRACT
COMMITMENT_CORE_CONTRACT
SOROBAN_COMMITMENT_CORE_CONTRACT
Reads all sensitive inputs from environment variables only
Supports DRY_RUN=1 for safe local verification
Added deployment scaffolding and docs

contracts/Cargo.toml
contracts/.gitignore
contracts/README.md
Added a zero-dependency smoke test

contracts/scripts/deploy-testnet.smoke.mjs
Verifies dry-run behavior, env-file updates, and missing-input guardrails
Updated repo docs/config notes

.env.example
docs/config.md
package.json with test:contracts:deploy
Why
Before this change, there was no scripted way to build, deploy, initialize, and wire the contract id into the frontend/backend env configuration. This PR makes that flow repeatable and safer for testnet deployments.

Validation
Ran:

npm run test:contracts:deploy
Output:

deploy-testnet.sh dry-run smoke test passed

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