Add transaction reconciliation report generator

[Lex-Studios]

Implements #172

• Compares DB transactions with on-chain Stellar payments
• Identifies missing transactions, orphaned payments, amount mismatches
• CLI command: tx reconcile --start --end
• Supports JSON and text output formats
• Efficient memo-based matching

Files:

• src/services/reconciliation.rs - Reconciliation service
• src/cli.rs - CLI command handler
• src/main.rs - Command routing

Closes #172