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

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

openspec/changes/archive/2025-12-12-fix-ocr-track-reflow-pdf/specs/result-export/spec.md

@@ -0,0 +1,23 @@
+## MODIFIED Requirements
+
+### Requirement: Enhanced PDF Export with Layout Preservation
+
+The PDF export SHALL accurately preserve document layout from both OCR and direct extraction tracks with correct coordinate transformation and multi-page support. For Direct Track, a background image rendering approach SHALL be used for visual fidelity.
+
+#### Scenario: OCR Track reflow PDF uses raw OCR regions
+- **WHEN** generating reflow PDF for an OCR Track document
+- **THEN** the system SHALL load text content from `raw_ocr_regions.json` files
+- **AND** text blocks SHALL be sorted by Y coordinate for reading order
+- **AND** all text content SHALL match the Layout PDF output
+- **AND** images and charts SHALL be embedded from element `saved_path`
+
+#### Scenario: Direct Track reflow PDF uses structured content
+- **WHEN** generating reflow PDF for a Direct Track document
+- **THEN** the system SHALL use `content.cells` for table rendering
+- **AND** text elements SHALL use `content` string directly
+- **AND** images and charts SHALL be embedded from element `saved_path`
+
+#### Scenario: Reflow PDF content consistency
+- **WHEN** comparing Layout PDF and Reflow PDF for the same document
+- **THEN** both PDFs SHALL contain the same text content
+- **AND** only the presentation format SHALL differ (positioned vs flowing)