Fix parser line grouping across page breaks

[jasanpe]

Summary

• Preserve the PDF page number on parsed text items.
• Flush the current line when text extraction moves to a new page, so a section heading at the top of the next page cannot be merged into the previous page's last line.
• Add a regression test covering the page-break case and verifying the next-page heading is recognized as its own section.

Fixes #174.

Verification

• npx jest src/app/lib/parse-resume-from-pdf/group-text-items-into-lines.test.ts --ci --runInBand
• npm run test:ci -- --runInBand
• npm run lint (passes with existing react-hooks/exhaustive-deps warning in src/app/lib/redux/hooks.tsx)
• npm run build (passes with the same existing lint warning)

Note: npx tsc --noEmit currently reports missing module declarations for existing SVG/JPG imports under public/, while next build completes its normal type-check/build path successfully.