[Feature Request]: migrate pdf.js to pdfium for file analyzer

[Frooodle]

Feature Description

fileAnalyzer uses pdfWorkerManager (PDF.js) for isPDFUserPasswordProtected() and quickPDFAnalysis().
Encryption detection only needs a header scan; corruption checks can ride on the PDFium load result. Move both onto @embedpdf/engines so this stops being a pdfjs-dist consumer.

Files:

• frontend/src/core/services/fileAnalyzer.ts

Acceptance:

• No pdfjs-dist or pdfWorkerManager imports.
• Upload validation behaves the same on encrypted, corrupted, and clean PDFs.

Why is this feature valuable?

No response

Suggested Implementation

No response

Additional Information

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No Duplicate of the Feature

• I have verified that there are no existing features requests similar to my request.