feat: enable document orientation detection for scanned PDFs

- Enable PP-StructureV3's use_doc_orientation_classify feature
- Detect rotation angle from doc_preprocessor_res.angle
- Swap page dimensions (width <-> height) for 90°/270° rotations
- Output PDF now correctly displays landscape-scanned content

Also includes:
- Archive completed openspec proposals
- Add simplify-frontend-ocr-config proposal (pending)
- Code cleanup and frontend simplification

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

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

openspec/changes/archive/2025-12-11-fix-table-column-alignment/proposal.md

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+# Change: Fix Table Column Alignment with Header-Anchor Correction
+
+## Why
+
+PP-Structure's table structure recognition frequently outputs cells with incorrect column indices, causing "column shift" where content appears in the wrong column. This happens because:
+
+1. **Semantic over Geometric**: The model infers row/col from semantic patterns rather than physical coordinates
+2. **Vertical text fragmentation**: Chinese vertical text (e.g., "报价内容") gets split into fragments
+3. **Missing left boundary**: When table's left border is unclear, cells shift left incorrectly
+
+The result: A cell with X-coordinate 213 gets assigned to column 0 (range 96-162) instead of column 1 (range 204-313).
+
+## What Changes
+
+- **Add Header-Anchor Alignment**: Use the first row (header) X-coordinates as column reference points
+- **Add Coordinate-Based Column Correction**: Validate and correct cell column assignments based on X-coordinate overlap with header columns
+- **Add Vertical Fragment Merging**: Detect and merge vertically stacked narrow text blocks that represent vertical text
+- **Add Configuration Options**: Enable/disable correction features independently
+
+## Impact
+
+- Affected specs: `document-processing`
+- Affected code:
+  - `backend/app/services/table_column_corrector.py` (new)
+  - `backend/app/services/pdf_generator_service.py`
+  - `backend/app/core/config.py`
+
+## Problem Analysis
+
+### Example: scan.pdf Table 7
+
+**Raw PP-Structure Output:**
+```
+Row 5: "3、適應產品..." at X=213
+       Model says: col=0
+
+Header Row 0:
+  - Column 0 (序號): X range [96, 162]
+  - Column 1 (產品名稱): X range [204, 313]
+```
+
+**Problem:** X=213 is far outside column 0's range (max 162), but perfectly within column 1's range (starts at 204).
+
+**Solution:** Force-correct col=0 → col=1 based on X-coordinate alignment with header.
+
+### Vertical Text Issue
+
+**Raw OCR:**
+```
+Block A: "报价内" at X≈100, Y=[100, 200]
+Block B: "容--"   at X≈102, Y=[200, 300]
+```
+
+**Problem:** These should be one cell spanning multiple rows, but appear as separate fragments.
+
+**Solution:** Merge vertically aligned narrow blocks before structure recognition.