feat(grid-editor): add manual cell color control via right-click menu

Users can now right-click any cell to set text color (red, green, blue,
orange, purple, black) or remove the color bar without changing text.
A "reset" option restores the OCR-detected color. This enables accurate
Ground Truth marking when OCR assigns colors to wrong cells.

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

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

@@ -56,6 +56,7 @@ export function StepGridReview({ sessionId, onNext, saveRef }: StepGridReviewPro
     clearCellSelection,
     toggleSelectedBold,
     autoCorrectColumnPatterns,
+    setCellColor,
   } = useGridEditor(sessionId)
 
   const [showImage, setShowImage] = useState(true)
@@ -399,6 +400,7 @@ export function StepGridReview({ sessionId, onNext, saveRef }: StepGridReviewPro
                           onAddColumn={addColumn}
                           onDeleteRow={deleteRow}
                           onAddRow={addRow}
+                          onSetCellColor={setCellColor}
                         />
                       </div>
                     ))}
@@ -438,6 +440,7 @@ export function StepGridReview({ sessionId, onNext, saveRef }: StepGridReviewPro
           <span>Pfeiltasten: Navigation</span>
           <span>Ctrl+Klick: Mehrfachauswahl</span>
           <span>Ctrl+B: Fett</span>
+          <span>Rechtsklick: Farbe</span>
           <span>Ctrl+Z/Y: Undo/Redo</span>
           <span>Ctrl+S: Speichern</span>
         </div>