Implement Recurring Transactions Table

[pyang4s]

Description:
Add support for recurring transactions (monthly bills, salaries) to avoid manual data entry.

Acceptance Criteria:

• Create recurring_transactions table with frequency field
• Add fields: person_id, category_id, amount, frequency (daily/weekly/monthly/yearly), start_date, end_date
• Create script scripts/generate_recurring.sh to auto-generate transactions
• Add sample recurring transactions to sample_data.sql
• Update schema documentation
• Add usage instructions to README

Estimated Effort: 3-4 hours