feat(app): add document (PDF) memory support

[comppaz]

Summary

• Add complete document (PDF) memory feature with encrypted storage and AI processing
• Upload PDFs with text extraction and thumbnail generation
• Encrypted document storage using Fernet encryption
• AI-powered title, summary, and tag generation
• PDF viewer with pagination in memory detail panel
• Open documents in system default application

Code Quality Improvements

• Extract Poppler version to workflow variable to prevent future CI/CD breakage
• Create shared useDocumentUpload hook to reduce code duplication
• Add error logging to Electron temp file cleanup
• Add empty PDF validation to reject image-only/scanned PDFs
• Simplify Vite PDF.js worker configuration

Test plan

• Upload a PDF document from HomePage
• Upload a PDF document from MemoriesPage
• Verify thumbnail is generated and displayed
• Verify text extraction works (check memory detail panel)
• Verify AI processing generates title, summary, and tags
• Open document in system viewer
• Try uploading an image-only PDF (should be rejected)
• Verify CI/CD workflow syntax is valid