fix: OCR Track reflow PDF and translation with image text filtering

- Add OCR Track support for reflow PDF generation using raw_ocr_regions.json
- Add OCR Track translation extraction from raw_ocr_regions instead of elements
- Add raw_ocr_translations output format for OCR Track documents
- Add exclusion zone filtering to remove text overlapping with images
- Update API validation to accept both translations and raw_ocr_translations
- Add page_number field to TranslatedItem for proper tracking

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2025-12-12-fix-ocr-track-reflow-pdf/tasks.md

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+# Tasks: Fix OCR Track Reflow PDF
+
+## 1. Modify generate_reflow_pdf Method
+
+- [x] 1.1 Add processing track detection
+  - File: `backend/app/services/pdf_generator_service.py`
+  - Location: `generate_reflow_pdf` method (line ~4704)
+  - Read `metadata.processing_track` from JSON data
+  - Branch logic based on track type
+
+- [x] 1.2 Add helper function to load raw OCR regions
+  - File: `backend/app/services/pdf_generator_service.py`
+  - Using existing: `load_raw_ocr_regions` from `text_region_renderer.py`
+  - Pattern: `{task_id}_*_page_{page_num}_raw_ocr_regions.json`
+  - Return: List of text regions with bbox and content
+
+- [x] 1.3 Implement OCR Track reflow rendering
+  - File: `backend/app/services/pdf_generator_service.py`
+  - For OCR Track: Load raw OCR regions per page
+  - Sort text blocks by Y coordinate (top to bottom reading order)
+  - Render text blocks as paragraphs
+  - Still render images/charts from elements
+
+- [x] 1.4 Keep Direct Track logic unchanged
+  - File: `backend/app/services/pdf_generator_service.py`
+  - Direct Track continues using `content.cells` for tables
+  - Extracted to `_render_reflow_elements` helper method
+  - No changes to existing Direct Track flow
+
+## 2. Handle Multi-page Documents
+
+- [x] 2.1 Support per-page raw OCR files
+  - Pattern: `{task_id}_*_page_{page_num}_raw_ocr_regions.json`
+  - Iterate through pages and load corresponding raw OCR file
+  - Handle missing files gracefully (fall back to elements)
+
+## 3. Testing
+
+- [x] 3.1 Test OCR Track reflow PDF
+  - Test with: `a9259180-fc49-4890-8184-2e6d5f4edad3` (scan document)
+  - Verify: All 59 text blocks appear in reflow PDF
+  - Verify: Images are embedded correctly
+
+- [x] 3.2 Test Direct Track reflow PDF
+  - Test with: `1b32428d-0609-4cfd-bc52-56be6956ac2e` (editable PDF)
+  - Verify: Tables render with cells
+  - Verify: No regression from changes
+
+- [x] 3.3 Test translated reflow PDF
+  - Test: Complete translation then download reflow PDF
+  - Verify: Translated text appears correctly