feat(contract): add get_protocol_fee_view read-only view method

[sshdopey]

Summary

Adds a dedicated get_protocol_fee_view method that returns a stable, non-optional ProtocolFeeView struct for indexer-friendly consumption of the current protocol fee configuration.

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

Checklist

• Linked issue or backlog item
• Contract behavior and invariants are described clearly
• Docs updated if contract interfaces or workflows changed
• Scope stays limited to one contract concern

Issues Resolved

Closes #19

Changes

#19 - Add read-only protocol fee config view method

Added ProtocolFeeView { creator_bps, protocol_bps, is_configured } struct and get_protocol_fee_view method to CreatorKeysContract. Unlike the existing get_fee_config which returns Option<FeeConfig>, this method always returns a value: is_configured is false and both bps fields are 0 when no config is stored. Added tests/fee_config_view.rs with 4 tests covering the unconfigured state, configured values, read-only idempotency, and reconfiguration.

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