Fix calculateVat/calculateTotal to use proper monetary rounding. Add
getVatSummaryFromItems helper for deriving VAT labels from mixed-rate items.
Update invoice preview, review, and detail pages to show per-rate VAT
breakdown instead of a single aggregated rate.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Merge the singular lib/invoice/ directory into the plural lib/invoices/
to align with the codebase convention (transactions/, extensions/, reports/, etc.).
Updates all import paths and CLAUDE.md architecture docs.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>