feat: Add PDF export for Income Statement and Tax Report

[Samanyu-dev]

Description

This PR implements the missing PDF export functionality for both the Income Statement and Tax Report pages. It integrates jspdf and jspdf-autotable to generate professionally formatted PDF documents client-side using the data already fetched via route loaders.

Specific Changes:

• Income Statement Export: Wired the "Export PDF" button to trigger a client-side download of fliptrack_income_statement.pdf. The generated document includes a summary table (Revenue, COGS, Gross Profit, Platform/Shipping fees, Net Profit), a monthly breakdown, and a detailed line-item expense log.
• Tax Report Export: Plumbed sales and expenses loader data down to the ExportOptions component. Replaced the disabled state of the "PDF Report" button with an active click handler downloading fliptrack_tax_report_{taxYear}.pdf, which encompasses a tax summary and a detailed breakdown of deductible business expenses.

Related Issues

Fixes #7

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

Screenshots (if applicable)

(N/A - Data exports only, no primary UI changes)

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