Ticket checkout acceleration pass: escrow/split wrappers + deploy/invoke completion + coverage gate

[inteee]

Summary

This PR delivers the smallest practical implementation to close the assigned escrow/split helper and CI script/coverage gaps.

Included

• Added ticket_escrow helper wrapper for ticket purchase escrow setup.
• Added revenue_split helper wrapper for organizer/artist/platform payout distribution.
• Added focused tests covering both helpers through existing release/distribution paths.
• Updated scripts/deploy.sh to use required account env, testnet default, veritixpay.wasm, and .contract-id output.
• Updated scripts/invoke.sh to read .contract-id automatically and support $ARGS forwarding.
• Added CI coverage workflow steps via cargo-llvm-cov with 80% minimum enforcement.
• Added coverage badge to README.

Notes

• Changes are intentionally thin wrappers over existing escrow/multi-escrow logic with no new storage model.

Closes #230
Closes #231
Closes #232
Closes #233

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