fix: resolve compile errors in fees.rs and main.rs (Phase 0)

[northersubair]

Summary

Phase 0 of API contract consistency - fixes blocking compile errors.

Changes

• Adds missing closing brace to account_fee_history in fees.rs
• Splits multi-argument .route() call in main.rs into two separate routes
• Adds #[derive(Serialize, Deserialize)] to TransactionFeeResponse

Closes #552