fix: add image_regions and tables to bbox dimension calculation

Critical Fix - Complete Solution:
Previous fix missed image_regions and tables fields, causing incorrect
scale factors when images or tables extended beyond text regions.

User's Scenario (multiple JSON files):
- text_regions: max coordinates ~1850
- image_regions: max coordinates ~2204 (beyond text!)
- tables: max coordinates ~3500 (beyond both!)
- Without checking all fields → scale=1.0 → content out of bounds

Complete Fix:
Now checks ALL possible bbox sources:
1. text_regions - text content
2. image_regions - images/figures/charts (NEW)
3. tables - table structures (NEW)
4. layout - legacy field
5. layout_data.elements - PP-StructureV3 format

Changes:
- backend/app/services/pdf_generator_service.py:
  - Add image_regions check (critical for images at X=1434, X=2204)
  - Add tables check (critical for tables at Y=3500)
  - Add type checks for all fields for safety
  - Update warning message to list all checked fields

- backend/test_all_regions.py:
  - Test all region types are properly checked
  - Validates max dimensions from ALL sources
  - Confirms correct scale factors (~0.27, ~0.24)

Test Results:
✓ All 5 regions checked (text + image + table)
✓ OCR dimensions: 2204 x 3500 (from ALL regions)
✓ Scale factors: X=0.270, Y=0.241 (correct!)

This is the COMPLETE fix for the dimension inference bug.

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

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

backend/app/services/pdf_generator_service.py

@@ -158,14 +158,22 @@ class PDFGeneratorService:
         all_regions = []
 
         # 1. text_regions - 包含所有文字區域（最常見）
-        if 'text_regions' in ocr_data:
+        if 'text_regions' in ocr_data and isinstance(ocr_data['text_regions'], list):
             all_regions.extend(ocr_data['text_regions'])
 
-        # 2. layout - 可能包含布局信息
+        # 2. image_regions - 包含圖片區域
+        if 'image_regions' in ocr_data and isinstance(ocr_data['image_regions'], list):
+            all_regions.extend(ocr_data['image_regions'])
+
+        # 3. tables - 包含表格區域
+        if 'tables' in ocr_data and isinstance(ocr_data['tables'], list):
+            all_regions.extend(ocr_data['tables'])
+
+        # 4. layout - 可能包含布局信息（可能是空列表）
         if 'layout' in ocr_data and isinstance(ocr_data['layout'], list):
             all_regions.extend(ocr_data['layout'])
 
-        # 3. layout_data.elements - PP-StructureV3 格式
+        # 5. layout_data.elements - PP-StructureV3 格式
         if 'layout_data' in ocr_data and isinstance(ocr_data['layout_data'], dict):
             elements = ocr_data['layout_data'].get('elements', [])
             if elements:
@@ -173,7 +181,7 @@ class PDFGeneratorService:
 
         if not all_regions:
             # 如果 JSON 為空，回退到原始檔案尺寸
-            logger.warning("JSON 中沒有找到任何包含 bbox 的區域，回退到原始檔案尺寸。")
+            logger.warning("JSON 中沒有找到 text_regions, image_regions, tables, layout 或 layout_data.elements，回退到原始檔案尺寸。")
             if source_file_path:
                 dims = self.get_original_page_size(source_file_path)
                 if dims: