Fix gutter repair: detect short fragments + show spell alternatives

- Lower min word length from 3→2 for hyphen-join candidates so fragments
  like "ve" (from "ver-künden") are no longer skipped
- Return all spellchecker candidates instead of just top-1, so user can
  pick the correct form (e.g. "stammeln" vs "stammelt")
- Frontend shows clickable alternative buttons for spell_fix suggestions
- Backend accepts text_overrides in apply endpoint for user-selected alternatives

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

klausur-service/backend/grid_editor_api.py

@@ -1923,9 +1923,20 @@ async def gutter_repair_apply(session_id: str, request: Request):
     if not accepted_ids:
         return {"applied_count": 0, "changes": []}
 
+    # text_overrides: { suggestion_id: "alternative_text" }
+    # Allows the user to pick a different correction from the alternatives list
+    text_overrides = body.get("text_overrides", {})
+
     from cv_gutter_repair import apply_gutter_suggestions
 
     suggestions = gutter_result.get("suggestions", [])
+
+    # Apply user-selected alternatives before passing to apply
+    for s in suggestions:
+        sid = s.get("id", "")
+        if sid in text_overrides and text_overrides[sid]:
+            s["suggested_text"] = text_overrides[sid]
+
     result = apply_gutter_suggestions(grid_data, accepted_ids, suggestions)
 
     # Save updated grid back to session