test: add sell quote vs execution proceeds regression

[wheval]

Summary

Adds a regression test that calls get_sell_quote before sell_key and asserts the quoted seller net (total_amount) exactly matches proceeds derived from the execution fee path, with zero divergence.

Purpose / Motivation

Sell quotes and sell execution use separate code paths. A mismatch between the quoted payout and the fees applied at execution would break client trust and can cause financial discrepancies. This test closes that gap by verifying both paths agree for the same (creator, holder) inputs.

Changes Made

• New integration test creator-keys/tests/sell_quote_matches_execution.rs
• Covers two supply levels (1 and 5 keys) before the sell
• Asserts quote.total_amount equals execution-path net proceeds (price - fees) before and after sell_key
• Asserts the difference between quoted and actual proceeds is exactly zero

How to Test

1. From the repo root: cargo test -p creator-keys --test sell_quote_matches_execution
2. Expected: both test_sell_quote_proceeds_match_execution_at_supply_one and test_sell_quote_proceeds_match_execution_at_supply_five pass
3. Optional full suite: cargo test -p creator-keys

Screenshots (if applicable)

N/A — contract tests only.

Breaking Changes

• None.

Related Issues

Closes #304

Checklist

• Code builds successfully
• Tests added/updated
• No console errors
• Documentation updated (if needed)

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