Merge remote v4/v5 features (multimodal chat input, layered generation, annotation detection) with local v3 features (dialog file upload, XLSX support, session fix)

Key resolutions:
- agent/nodes.py: Merged session_id exclusion fix with new persistable fields (ocr_extraction_result, annotation_result, layout_schema, ocr_elements)
- app.py: Adopted st-multimodal-chatinput for unified paste/drop/upload, removed custom JS paste bridge
- backend/file_parser.py: Kept local XLSX parser, added remote XLS/DOC parsers
- CLAUDE.md + CODE_GUIDE.md: Merged documentation from both branches

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

requirements.txt

@@ -27,6 +27,24 @@ httpx>=0.27.0
 tiktoken>=0.7.0
 openpyxl>=3.1.0
 
+# OCR 依赖（PaddleOCR 精确识别优先，EasyOCR 回退）
+# Pinned: paddleocr 2.9.x + paddlepaddle 2.6.x known-stable on Windows CPU
+# 3.x has ONEDNN compatibility issues on Windows
+paddleocr>=2.9.0,<3.0.0
+paddlepaddle>=2.6.0,<3.0.0
+easyocr>=1.7.0
+# 聊天输入增强（粘贴/拖拽上传）
+st-multimodal-chatinput>=0.2.1
+
+# 多格式文件解析
+openpyxl>=3.1.0
+xlrd>=2.0.0
+olefile>=0.47
+
+# 批注检测（圈选/箭头识别）
+opencv-python-headless>=4.8.0
+
 # 测试
 pytest>=8.0.0
 pytest-asyncio>=0.24.0
+xlwt>=1.3.0