feat(ocr-pipeline): ground-truth comparison tool for column detection

Side-by-side view: auto result (readonly) vs GT editor where teacher
draws correct columns. Diff table shows Auto vs GT with IoU matching.
GT data persisted per session for algorithm tuning.

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

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

@@ -81,6 +81,7 @@ export interface ColumnResult {
 
 export interface ColumnGroundTruth {
   is_correct: boolean
+  corrected_columns?: PageRegion[]
   notes?: string
 }