feat(market): add secondary market support for tradeable reward NFTs

[Deyanju23]

Closes #346

Summary

Implement the core secondary market for tradeable reward NFTs.

Changes

• Added the minimal persistent storage required for secondary-market state.
• Implemented core marketplace actions.
• Added authorization and ownership validation.
• Exposed the required functions through ShadeTrait.
• Added marketplace events for off-chain indexing.
• Added/updated tests covering marketplace behavior.

Why

Tradeable reward NFTs allow backers to transfer ownership after minting while remaining compatible with the existing fundraising system. This implementation focuses on the minimum secure functionality required without introducing additional marketplace features.

Testing

Covered:

• Successful marketplace flow
• Authorization failures
• Ownership validation
• Invalid listings
• Duplicate purchase protection
• Event emission
• Storage updates

Validation:

cargo test
cargo clippy --workspace --all-targets -- -D warnings
cargo build --target wasm32-unknown-unknown --release

Scope

This PR implements only the core secondary-market functionality. It intentionally excludes auctions, bidding, royalties, advanced marketplace features, and unrelated refactoring.

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