fix(ocr-pipeline): dewarp visibility, grid on both sides, session persistence

- Fix dewarp method selection: prefer methods with >5px curvature over
  higher confidence (vertical_edge 79px was being ignored for text_baseline 2px)
- Add grid overlay on left image in Dewarp step for side-by-side comparison
- Add GET /sessions/{id} endpoint to reload session data
- StepDeskew accepts sessionId prop to restore state when navigating back
- SessionInfo type extended with optional deskew_result and dewarp_result

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

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

@@ -9,6 +9,7 @@ interface ImageCompareViewProps {
   originalUrl: string | null
   deskewedUrl: string | null
   showGrid: boolean
+  showGridLeft?: boolean
   showBinarized: boolean
   binarizedUrl: string | null
   leftLabel?: string
@@ -77,6 +78,7 @@ export function ImageCompareView({
   originalUrl,
   deskewedUrl,
   showGrid,
+  showGridLeft,
   showBinarized,
   binarizedUrl,
   leftLabel,
@@ -95,12 +97,15 @@ export function ImageCompareView({
         <div className="relative bg-gray-100 dark:bg-gray-900 rounded-lg overflow-hidden border border-gray-200 dark:border-gray-700"
              style={{ aspectRatio: '210/297' }}>
           {originalUrl && !leftError ? (
-            <img
-              src={originalUrl}
-              alt="Original Scan"
-              className="w-full h-full object-contain"
-              onError={() => setLeftError(true)}
-            />
+            <>
+              <img
+                src={originalUrl}
+                alt="Original Scan"
+                className="w-full h-full object-contain"
+                onError={() => setLeftError(true)}
+              />
+              {showGridLeft && <MmGridOverlay />}
+            </>
           ) : (
             <div className="flex items-center justify-center h-full text-gray-400">
               {leftError ? 'Fehler beim Laden' : 'Noch kein Bild'}