refactor(word-step): make table fully generic and fix marker-only row filter

Frontend: Replace hardcoded EN/DE/Example vocab table with unified dynamic
table driven by columns_used from backend. Labeling, confirmation, counts,
and summary badges are now all cell-based instead of branching on isVocab.

Backend: Change _cells_to_vocab_entries() entry filter from checking only
english/german/example to checking ANY mapped field. This preserves rows
with only marker or source_page content, fixing the issue where marker
sub-columns disappeared at the end of OCR processing.

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

klausur-service/backend/cv_vocab_pipeline.py

@@ -4281,8 +4281,12 @@ def _cells_to_vocab_entries(
             sum(confidences) / len(confidences), 1
         ) if confidences else 0.0
 
-        # Only include if at least one vocab field has text
-        if entry['english'] or entry['german'] or entry['example']:
+        # Only include if at least one mapped field has text
+        has_content = any(
+            entry.get(f)
+            for f in col_type_to_field.values()
+        )
+        if has_content:
             entries.append(entry)
 
     return entries