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>

frontend/src/components/TableDetectionSelector.tsx

@@ -0,0 +1,124 @@
+import { cn } from '@/lib/utils'
+import { Checkbox } from '@/components/ui/checkbox'
+import { Table, Grid3X3, Rows3 } from 'lucide-react'
+import { useTranslation } from 'react-i18next'
+import type { TableDetectionConfig } from '@/types/apiV2'
+
+interface TableDetectionSelectorProps {
+  value: TableDetectionConfig
+  onChange: (config: TableDetectionConfig) => void
+  disabled?: boolean
+  className?: string
+}
+
+interface DetectionOption {
+  key: keyof TableDetectionConfig
+  icon: React.ReactNode
+  labelKey: string
+  descKey: string
+}
+
+const DETECTION_OPTIONS: DetectionOption[] = [
+  {
+    key: 'enable_wired_table',
+    icon: <Grid3X3 className="w-5 h-5" />,
+    labelKey: 'processing.tableDetection.wired',
+    descKey: 'processing.tableDetection.wiredDesc',
+  },
+  {
+    key: 'enable_wireless_table',
+    icon: <Rows3 className="w-5 h-5" />,
+    labelKey: 'processing.tableDetection.wireless',
+    descKey: 'processing.tableDetection.wirelessDesc',
+  },
+  {
+    key: 'enable_region_detection',
+    icon: <Table className="w-5 h-5" />,
+    labelKey: 'processing.tableDetection.region',
+    descKey: 'processing.tableDetection.regionDesc',
+  },
+]
+
+export default function TableDetectionSelector({
+  value,
+  onChange,
+  disabled = false,
+  className,
+}: TableDetectionSelectorProps) {
+  const { t } = useTranslation()
+
+  const handleOptionChange = (key: keyof TableDetectionConfig, checked: boolean) => {
+    onChange({
+      ...value,
+      [key]: checked,
+    })
+  }
+
+  return (
+    <div className={cn('border rounded-lg p-4 bg-white', className)}>
+      {/* Header */}
+      <div className="flex items-center gap-2 mb-4">
+        <Table className="w-5 h-5 text-gray-600" />
+        <h3 className="text-lg font-semibold text-gray-900">{t('processing.tableDetection.title')}</h3>
+      </div>
+
+      {/* Detection Options */}
+      <div className="space-y-3">
+        {DETECTION_OPTIONS.map((option) => {
+          const isChecked = value[option.key]
+
+          return (
+            <label
+              key={option.key}
+              className={cn(
+                'flex items-start gap-4 p-4 rounded-lg border-2 transition-all cursor-pointer',
+                isChecked
+                  ? 'border-blue-500 bg-blue-50'
+                  : 'border-gray-200 hover:border-gray-300 hover:bg-gray-50',
+                disabled && 'opacity-50 cursor-not-allowed'
+              )}
+            >
+              {/* Checkbox */}
+              <Checkbox
+                checked={isChecked}
+                onCheckedChange={(checked) => handleOptionChange(option.key, checked)}
+                disabled={disabled}
+                className="mt-0.5"
+              />
+
+              {/* Icon */}
+              <div
+                className={cn(
+                  'p-2 rounded-lg flex-shrink-0',
+                  isChecked ? 'bg-blue-100 text-blue-600' : 'bg-gray-100 text-gray-500'
+                )}
+              >
+                {option.icon}
+              </div>
+
+              {/* Content */}
+              <div className="flex-1 min-w-0">
+                <span
+                  className={cn(
+                    'font-medium',
+                    isChecked ? 'text-blue-700' : 'text-gray-900'
+                  )}
+                >
+                  {t(option.labelKey)}
+                </span>
+                <p className="text-sm text-gray-500 mt-1">{t(option.descKey)}</p>
+              </div>
+            </label>
+          )
+        })}
+      </div>
+
+      {/* Info Note */}
+      <div className="mt-4 p-3 bg-amber-50 border border-amber-200 rounded-md">
+        <p className="text-sm text-amber-800">
+          {t('processing.tableDetection.note')}
+        </p>
+      </div>
+    </div>
+  )
+}