fix: resolve blank slides and broken links in server-side PDF export (#10501)

[Jacopos311]

Closes #10501

📝 Summary

This pull request resolves an issue where exporting slide decks containing plots or interactive outputs to PDF resulted in blank slides or broken links.

Specific Changes Made:

• Server Endpoint (marimo/_server/api/endpoints/export.py): Updated the export_as_pdf handler to collect PNG fallbacks via collect_pdf_png_fallbacks() when include_outputs is enabled and a session view is present. These fallbacks are now successfully passed down via PDFExportRequest, bringing the server-side export flow in line with the CLI flow.
• Virtual File Inlining (marimo/_export/exporter.py): Added _inline_virtual_files_in_notebook() to resolve ./@file/... virtual file references into inline data URIs inside notebook cell outputs prior to nbconvert processing. This ensures assets load correctly when rendered locally via file:// URIs.
• Playwright Dependency Check (marimo/_export/exporter.py): Added an explicit DependencyManager.playwright.require() check inside _export_slides_as_pdf() to ensure a clean, user-friendly error message if Playwright/Chromium binaries are missing, instead of a raw ModuleNotFoundError.
• Tests (tests/_export/test_exporter.py): Added dedicated unit tests covering slides PDF export with PNG fallbacks and virtual file inlining behavior.

📋 Pre-Review Checklist

• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Linked to Exporting slides including plots to PDF generates broken links #10501).
• Any AI generated code has been reviewed line-by-line by the human PR author, who stands by it.
• Video or media evidence is provided for any visual changes (optional).

✅ Merge Checklist

• I have read the contributor guidelines.
• Documentation has been updated where applicable, including docstrings for API changes.
• Tests have been added for the changes made.

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview	Aug 15, 2026 12:18am

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[Jacopos311]

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[Jacopos311]

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