Allow importing statements to accounts with active bank connections

Enable manual statement imports for accounts with active bank connections (Monobank, EnableBanking).

Use case: Fill gaps in bank sync history or import older statements that weren’t automatically synced.

Current limitation: Import is designed only for manual accounts without bank sync.

Requirements:

• Enhanced duplicate detection against bank-synced transactions

• Warn users about potential conflicts with automatic sync

• Allow import while maintaining bank connection integrity

• Prevent duplicate transactions when sync runs

Good for filling historical gaps or supplementing incomplete sync data.