feat: add translated PDF format selection (layout/reflow)

- Add generate_translated_layout_pdf() method for layout-preserving translated PDFs
- Add generate_translated_pdf() method for reflow translated PDFs
- Update translate router to accept format parameter (layout/reflow)
- Update frontend with dropdown to select translated PDF format
- Fix reflow PDF table cell extraction from content dict
- Add embedded images handling in reflow PDF tables
- Archive improve-translated-text-fitting openspec proposal

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

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

requirements.txt

@@ -10,8 +10,11 @@ email-validator>=2.0.0  # For pydantic EmailStr validation
 
 # ===== OCR Engine =====
 paddleocr>=3.0.0
-# paddlepaddle>=3.0.0  # Installed separately in setup script (GPU/CPU version)
 paddlex[ocr]>=3.0.0  # Required for PP-StructureV3 layout analysis
+# PaddlePaddle Installation (NOT available on PyPI for 3.x):
+#   GPU (CUDA 12.6): pip install paddlepaddle-gpu==3.2.0 -i https://www.paddlepaddle.org.cn/packages/stable/cu126/
+#   GPU (CUDA 12.9): pip install paddlepaddle-gpu==3.2.0 -i https://www.paddlepaddle.org.cn/packages/stable/cu129/
+#   CPU:             pip install paddlepaddle -i https://www.paddlepaddle.org.cn/packages/stable/cpu/
 
 # ===== Image Processing =====
 pillow>=10.0.0
@@ -28,7 +31,7 @@ PyPDF2>=3.0.0  # Extract dimensions from source PDF files
 # ===== Direct PDF Extraction (Dual-track Processing) =====
 PyMuPDF>=1.23.0  # Primary library for editable PDF text/structure extraction
 pdfplumber>=0.10.0  # Fallback for table extraction and validation
-python-magic-bin>=0.4.14  # Windows-compatible file type detection
+# Note: python-magic requires libmagic (apt install libmagic1 on Linux)
 
 # ===== Data Export =====
 pandas>=2.1.0
@@ -57,8 +60,9 @@ requests>=2.31.0
 # redis>=5.0.0  # Uncomment if using Redis for task queue
 # celery>=5.3.0  # Uncomment if using Celery
 
-# ===== Translation (Reserved) =====
-# argostranslate>=1.9.0  # Uncomment when implementing translation
+# ===== Translation =====
+# Translation will use external API (to be implemented)
+# See openspec/changes/add-document-translation/ for proposal
 
 # ===== Development Tools =====
 pytest>=7.4.0