[Feature Request]: migrate pdf.js to pdfium for metadata service

[Frooodle]

Feature Description

pdfMetadataService loads PDFs via pdfWorkerManager (PDF.js) to read numPages and metadata. Switch to @embedpdf/core for the active document and @embedpdf/engines (PDFium WASM) for off-screen reads, so this service no longer pulls in pdfjs-dist.

Files:

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

Acceptance:

• No pdfjs-dist or pdfWorkerManager imports remain in the file.
• Existing callers get the same metadata fields back.

Why is this feature valuable?

No response

Suggested Implementation

No response

Additional Information

No response

No Duplicate of the Feature

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