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/app/(admin)/ai/ocr-pipeline/page.tsx

@@ -49,7 +49,7 @@ export default function OcrPipelinePage() {
   const renderStep = () => {
     switch (currentStep) {
       case 0:
-        return <StepDeskew onNext={handleDeskewComplete} />
+        return <StepDeskew sessionId={sessionId} onNext={handleDeskewComplete} />
       case 1:
         return <StepDewarp sessionId={sessionId} onNext={handleNext} />
       case 2:

admin-lehrer/app/(admin)/ai/ocr-pipeline/types.ts

@@ -13,6 +13,8 @@ export interface SessionInfo {
   image_width: number
   image_height: number
   original_image_url: string
+  deskew_result?: DeskewResult
+  dewarp_result?: DewarpResult
 }
 
 export interface DeskewResult {