feat(ocr-pipeline): 6 systematic improvements for robustness, performance & UX

1. Unit tests: 76 new parametrized tests for noise filter, phonetic detection,
   cell text cleaning, and row merging (116 total, all green)
2. Continuation-row merge: detect multi-line vocab entries where text wraps
   (lowercase EN + empty DE) and merge into previous entry
3. Empty DE fallback: secondary PSM=7 OCR pass for cells missed by PSM=6
4. Batch-OCR: collect empty cells per column, run single Tesseract call on
   column strip instead of per-cell (~66% fewer calls for 3+ empty cells)
5. StepReconstruction UI: font scaling via naturalHeight, empty EN/DE field
   highlighting, undo/redo (Ctrl+Z), per-cell reset button
6. Session reprocess: POST /sessions/{id}/reprocess endpoint to re-run from
   any step, with reprocess button on completed pipeline steps

Also fixes pre-existing dewarp_image tuple unpacking bug in run_cv_pipeline
and updates dewarp tests to match current (image, info) return signature.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

admin-lehrer/components/ocr-pipeline/PipelineStepper.tsx

@@ -6,9 +6,10 @@ interface PipelineStepperProps {
   steps: PipelineStep[]
   currentStep: number
   onStepClick: (index: number) => void
+  onReprocess?: (index: number) => void
 }
 
-export function PipelineStepper({ steps, currentStep, onStepClick }: PipelineStepperProps) {
+export function PipelineStepper({ steps, currentStep, onStepClick, onReprocess }: PipelineStepperProps) {
   return (
     <div className="flex items-center justify-between px-4 py-3 bg-white dark:bg-gray-800 rounded-lg border border-gray-200 dark:border-gray-700">
       {steps.map((step, index) => {
@@ -26,25 +27,37 @@ export function PipelineStepper({ steps, currentStep, onStepClick }: PipelineSte
                 }`}
               />
             )}
-            <button
-              onClick={() => isClickable && onStepClick(index)}
-              disabled={!isClickable}
-              className={`flex items-center gap-1.5 px-3 py-1.5 rounded-full text-sm font-medium transition-all ${
-                isActive
-                  ? 'bg-teal-100 text-teal-700 dark:bg-teal-900/40 dark:text-teal-300 ring-2 ring-teal-400'
-                  : isCompleted
-                    ? 'bg-green-100 text-green-700 dark:bg-green-900/40 dark:text-green-300'
-                    : isFailed
-                      ? 'bg-red-100 text-red-700 dark:bg-red-900/40 dark:text-red-300'
-                      : 'text-gray-400 dark:text-gray-500'
-              } ${isClickable ? 'cursor-pointer hover:opacity-80' : 'cursor-default'}`}
-            >
-              <span className="text-base">
-                {isCompleted ? '✓' : isFailed ? '✗' : step.icon}
-              </span>
-              <span className="hidden sm:inline">{step.name}</span>
-              <span className="sm:hidden">{index + 1}</span>
-            </button>
+            <div className="relative group">
+              <button
+                onClick={() => isClickable && onStepClick(index)}
+                disabled={!isClickable}
+                className={`flex items-center gap-1.5 px-3 py-1.5 rounded-full text-sm font-medium transition-all ${
+                  isActive
+                    ? 'bg-teal-100 text-teal-700 dark:bg-teal-900/40 dark:text-teal-300 ring-2 ring-teal-400'
+                    : isCompleted
+                      ? 'bg-green-100 text-green-700 dark:bg-green-900/40 dark:text-green-300'
+                      : isFailed
+                        ? 'bg-red-100 text-red-700 dark:bg-red-900/40 dark:text-red-300'
+                        : 'text-gray-400 dark:text-gray-500'
+                } ${isClickable ? 'cursor-pointer hover:opacity-80' : 'cursor-default'}`}
+              >
+                <span className="text-base">
+                  {isCompleted ? '\u2713' : isFailed ? '\u2717' : step.icon}
+                </span>
+                <span className="hidden sm:inline">{step.name}</span>
+                <span className="sm:hidden">{index + 1}</span>
+              </button>
+              {/* Reprocess button — shown on completed steps on hover */}
+              {isCompleted && onReprocess && (
+                <button
+                  onClick={(e) => { e.stopPropagation(); onReprocess(index) }}
+                  className="absolute -top-1 -right-1 w-4 h-4 bg-orange-500 text-white rounded-full text-[9px] leading-none opacity-0 group-hover:opacity-100 transition-opacity flex items-center justify-center"
+                  title={`Ab hier neu verarbeiten`}
+                >
+                  &#x21BB;
+                </button>
+              )}
+            </div>
           </div>
         )
       })}