feat: configure soroban-cli for local development (#159)

[snowrugar-beep]

Summary

Closes #159

Sets up soroban-cli tooling and Makefile shortcuts so contributors can build, test, and deploy contracts locally with a single command.

Changes

Makefile

• make setup — installs stellar-cli via cargo and adds the wasm32-unknown-unknown target
• make sandbox-start — spins up a local Stellar sandbox via Docker (Quickstart image)
• make deploy-sandbox — builds WASM then deploys to the local sandbox
• make deploy-testnet — builds WASM then deploys to Stellar testnet
• All existing targets (build, test, fmt, lint, clean) preserved

scripts/deploy.sh

• Shared deploy script invoked by both deploy-sandbox and deploy-testnet
• Loads credentials from .env automatically
• Supports testnet, sandbox, and mainnet networks
• Idempotent: skips re-deploy if deployments/<network>.json already exists
• Saves deployment record to deployments/<network>.json (see Set up Soroban testnet deployment pipeline #160)

deployments/.gitkeep

• Tracks the deployments/ directory in git without committing JSON records

.gitignore

• Excludes deployments/*.json and .stellaraid_contract_id (network-specific artifacts)

Acceptance Criteria

Criterion	Status
soroban-cli installable via make setup	✅
Local sandbox configured via make sandbox-start	✅
make build compiles all contracts	✅ (existing, unchanged)
make deploy-sandbox deploys to local sandbox	✅
make deploy-testnet deploys to Stellar testnet	✅

Testing

# Install tooling
make setup

# Build contracts
make build

# Start local sandbox (requires Docker)
make sandbox-start

# Deploy locally
make deploy-sandbox

# Deploy to testnet (requires funded key in .env)
make deploy-testnet

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[ayshadogo]

LGTM

nice contribution