feat: add table detection options and scan artifact removal

- Add TableDetectionSelector component for wired/wireless/region detection
- Add CV-based table line detector module (disabled due to poor performance)
- Add scan artifact removal preprocessing step (removes faint horizontal lines)
- Add PreprocessingConfig schema with remove_scan_artifacts option
- Update frontend PreprocessingSettings with scan artifact toggle
- Integrate table detection config into ProcessingPage
- Archive extract-table-cell-boxes proposal

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

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

backend/app/schemas/task.py

@@ -96,6 +96,35 @@ class PreprocessingConfig(BaseModel):
         default=False,
         description="Enable binarization (aggressive, for very low contrast). Not recommended for most documents."
     )
+    remove_scan_artifacts: bool = Field(
+        default=True,
+        description="Remove horizontal scan line artifacts. Recommended for scanned documents to prevent misdetection of scanner light bar lines as table borders."
+    )
+
+
+class TableDetectionConfig(BaseModel):
+    """Table detection configuration for PP-StructureV3.
+
+    Controls which table detection modes to enable. PP-StructureV3 uses specialized
+    models for different table types:
+    - Wired (bordered): Tables with visible cell borders/grid lines
+    - Wireless (borderless): Tables without visible borders, relying on alignment
+    - Region detection: Detect table-like regions for better cell structure
+
+    Multiple options can be enabled simultaneously for comprehensive detection.
+    """
+    enable_wired_table: bool = Field(
+        default=True,
+        description="Enable wired (bordered) table detection. Best for tables with visible grid lines."
+    )
+    enable_wireless_table: bool = Field(
+        default=True,
+        description="Enable wireless (borderless) table detection. Best for tables without visible borders."
+    )
+    enable_region_detection: bool = Field(
+        default=True,
+        description="Enable region detection for better table structure inference."
+    )
 
 
 class ImageQualityMetrics(BaseModel):
@@ -294,6 +323,12 @@ class ProcessingOptions(BaseModel):
         description="Manual preprocessing config (only used when preprocessing_mode='manual')"
     )
 
+    # Table detection configuration (OCR track only)
+    table_detection: Optional[TableDetectionConfig] = Field(
+        None,
+        description="Table detection config. If None, all table detection modes are enabled."
+    )
+
 
 class AnalyzeRequest(BaseModel):
     """Document analysis request"""