Add A/B testing toggles to OCR Kombi Grid Review

Quality step toggles in admin-lehrer StepGridReview (port 3002):
- CLAHE checkbox (Step 3: image enhancement)
- MaxCol dropdown (Step 2: column limit, 0=off)
- MinConf dropdown (Step 1: OCR confidence, 0=auto)

Parameters flow through: StepGridReview → useGridEditor → build-grid
endpoint → _build_grid_core. MinConf filters words before grid building.

Toggle settings, click "Neu berechnen" to test each step individually.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/grid_editor_api.py

@@ -32,6 +32,9 @@ async def build_grid(
     session_id: str,
     ipa_mode: str = Query("auto", pattern="^(auto|all|de|en|none)$"),
     syllable_mode: str = Query("auto", pattern="^(auto|all|de|en|none)$"),
+    enhance: bool = Query(True, description="Step 3: CLAHE + denoise for degraded scans"),
+    max_cols: int = Query(0, description="Step 2: Max column count (0=unlimited)"),
+    min_conf: int = Query(0, description="Step 1: Min OCR confidence (0=auto)"),
 ):
     """Build a structured, zone-aware grid from existing Kombi word results.
 
@@ -53,6 +56,9 @@ async def build_grid(
         result = await _build_grid_core(
             session_id, session,
             ipa_mode=ipa_mode, syllable_mode=syllable_mode,
+            enhance=enhance,
+            max_columns=max_cols if max_cols > 0 else None,
+            min_conf=min_conf if min_conf > 0 else None,
         )
     except ValueError as e:
         raise HTTPException(status_code=400, detail=str(e))