fix(budget): suppress browser print chrome and render inner item separators (#1328)

[steilerDev]

Summary

• Expanded @page rule in BudgetOverviewPage.module.css with explicit empty content for all 10 CSS Paged Media margin boxes (@top-*/@bottom-*) — suppresses Chrome's injected header (date, page title) and footer (URL, page number) while preserving @page { margin: 1.5cm 1cm } for per-page whitespace
• Replaced non-rendering box-shadow: inset inner-box edges in CostBreakdownTable.module.css with border-top: 1pt solid var(--color-border) on .rowLevel2 td — creates visible item-group separators nested inside the outer area box

Fixes #1328

Test plan

• Unit tests pass (95%+ coverage)
• Integration tests pass
• Pre-commit hook quality gates pass

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com

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