feat: simplify layout model selection and archive proposals

Changes:
- Replace PP-Structure 7-slider parameter UI with simple 3-option layout model selector
- Add layout model mapping: chinese (PP-DocLayout-S), default (PubLayNet), cdla
- Add LayoutModelSelector component and zh-TW translations
- Fix "default" model behavior with sentinel value for PubLayNet
- Add gap filling service for OCR track coverage improvement
- Add PP-Structure debug utilities
- Archive completed/incomplete proposals:
  - add-ocr-track-gap-filling (complete)
  - fix-ocr-track-table-rendering (incomplete)
  - simplify-ppstructure-model-selection (22/25 tasks)
- Add new layout model tests, archive old PP-Structure param tests
- Update OpenSpec ocr-processing spec with layout model requirements

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

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

openspec/changes/fix-ocr-track-table-rendering/tasks.md

@@ -1,55 +0,0 @@
-# Implementation Tasks
-
-## Phase 1: Core Fix - Table Content Conversion
-
-### 1.1 Add TableData.from_dict() class method
-- [ ] In `unified_document.py`, add `from_dict()` method to `TableData` class
-- [ ] Handle conversion of cells list (list of dicts) to `TableCell` objects
-- [ ] Preserve rows, cols, headers, caption fields
-
-### 1.2 Fix _json_to_document_element for TABLE elements
-- [ ] In `pdf_generator_service.py`, modify `_json_to_document_element`
-- [ ] When `elem_type == ElementType.TABLE` and content is dict with 'cells', convert to `TableData`
-- [ ] Use `TableData.from_dict()` for clean conversion
-
-### 1.3 Verify TableData.to_html() generates correct HTML
-- [ ] Test that `to_html()` produces parseable HTML with proper row/cell structure
-- [ ] Verify colspan/rowspan attributes are correctly generated
-- [ ] Ensure empty cells are properly handled
-
-## Phase 2: OCR Track Rendering Consistency
-
-### 2.1 Review convert_unified_document_to_ocr_data
-- [ ] Verify TableData objects are properly converted to HTML
-- [ ] Add fallback handling for dict content with 'cells' key
-- [ ] Log warning if content cannot be converted to HTML
-
-### 2.2 Review draw_table_region
-- [ ] Verify HTMLTableParser correctly parses generated HTML
-- [ ] Check that ReportLab Table is positioned at correct bbox
-- [ ] Verify font and style application
-
-## Phase 3: Testing and Verification
-
-### 3.1 Test OCR Track
-- [ ] Test scan.pdf - verify tables have correct structure
-- [ ] Test img1.png, img2.png, img3.png
-- [ ] Compare generated PDF with original documents
-
-### 3.2 Test Direct Track (Regression)
-- [ ] Test PDF files with Direct track
-- [ ] Verify table rendering unchanged
-
-### 3.3 Test Hybrid Mode
-- [ ] Test files that trigger hybrid processing
-- [ ] Verify mixed Direct + OCR elements render correctly
-
-## Phase 4: Code Quality
-
-### 4.1 Add logging
-- [ ] Add debug logging for table content type detection
-- [ ] Log conversion steps for troubleshooting
-
-### 4.2 Error handling
-- [ ] Handle malformed cell data gracefully
-- [ ] Log warnings for unexpected content formats