docs: update all references from PyPDF2 to pypdf in documentation

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

docs/ConfigurationGuide.md

@@ -58,7 +58,7 @@ MAX_SINGLE_FILE_SIZE=524288000
 **File Splitting Behavior:**
 - When `MAX_SINGLE_FILE_SIZE` is configured and a PDF exceeds this size, it is automatically split into smaller chunks
 - **IMPORTANT:** Splitting is done at **PAGE BOUNDARIES**, not by byte position
-  - Uses PyPDF2 to properly parse PDF structure
+  - Uses pypdf to properly parse PDF structure
   - Each output file is a complete, valid PDF containing whole pages
   - No risk of corrupted or broken PDF files
   - Pages are distributed across output files to stay under size limit

docs/FileDetailPageLayout.md

@@ -15,7 +15,7 @@ POST /api/files/{id}/retry-subtask    → Retry specific task
 ## Text Extraction
 
 Text extraction is performed **on-demand** when the user clicks "View Extracted Text":
-- Uses PyPDF2 to extract text from PDF files in real-time
+- Uses pypdf to extract text from PDF files in real-time
 - Returns JSON: `{"text": "...", "page_count": 3}`
 - Client-side caching prevents re-extraction on subsequent views
 - Loading indicator shown during extraction

docs/UserGuide.md

@@ -182,7 +182,7 @@ Both previews support:
 - Full text extraction viewing via modal overlays
 
 **View Extracted Text**: Each preview includes a button to view the complete extracted text in a fullscreen modal. When you click this button:
-- The system extracts text from the PDF file on-demand using PyPDF2
+- The system extracts text from the PDF file on-demand using pypdf
 - A loading indicator shows while extraction is in progress
 - The extracted text is displayed in a scrollable, copy-friendly format
 - The text is cached so subsequent views load instantly

docs/archive/ANALYSIS_SUMMARY.md

@@ -230,7 +230,7 @@ httpx>=0.26.0
 
 ### Medium Priority (Next Month)
 - [ ] Fix Pydantic V1 → V2 migration warnings
-- [ ] Migrate from PyPDF2 to pypdf (modern fork)
+- [x] Migrate from PyPDF2 to pypdf (modern fork) - ✅ Completed 2026-02-12
 - [ ] Consolidate storage provider code
 - [ ] Add API pagination
 - [ ] Implement retry logic for Celery tasks