Add API service files and replace stub views with full implementations:
- Budgets: month navigator, budget items table with progress bars, create/edit/delete
- Scheduled Transactions: data table with skip/post-now actions, add/edit dialog
- Loans: loan list, detail view with amortization schedule, payoff scenario calculator
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>