fix(translate): three audit fixes — dict hash, SQL chunking, duplicate logic

1. dict_snapshot_hash now includes entry count + max(updated_at)
   per dictionary. Previously only hashed dictionary IDs, meaning
   edits to dictionary entries did NOT invalidate the translation
   cache. Stale cached translations could be served after editing
   dictionary entries. (HIGH severity)

2. _batch_insert.py now uses SQLGenerator.generate_batch() with
   500-row chunking instead of a single massive INSERT statement.
   Prevents potential SQL size limit issues with large batches or
   many target languages. (LOW severity)

3. Fixed same bug in preview_response_parser.py —
   compute_dict_snapshot_hash had identical ID-only hash flaw.

Tests: 69/69 translate tests pass.

backend/src/plugins/translate/_batch_insert.py

@@ -49,11 +49,25 @@ def insert_batch_to_target(
         if dialect is None:
             return
 
-        sql, row_count = _generate_insert_sql(dialect, job, columns, rows_for_sql, batch_id)
-        if sql is None:
-            return
-
-        _execute_insert_sql(executor, sql, batch_id, row_count)
+        # Use chunked INSERT to avoid SQL size limits (max 500 VALUES rows per statement)
+        statements = SQLGenerator.generate_batch(
+            dialect=dialect,
+            target_schema=job.target_schema,
+            target_table=job.target_table or "translated_data",
+            columns=columns,
+            rows=rows_for_sql,
+            key_columns=job.target_key_cols,
+            upsert_strategy=job.upsert_strategy or "MERGE",
+            max_rows_per_statement=500,
+        )
+        total_inserted = 0
+        for sql, chunk_count in statements:
+            if sql is None:
+                continue
+            _execute_insert_sql(executor, sql, batch_id, chunk_count)
+            total_inserted += chunk_count
+        logger.reason(f"Batch {batch_id[:12]} inserted {total_inserted} rows",
+                      {"batch_id": batch_id, "rows": total_inserted, "chunks": len(statements)})
 # #endregion insert_batch_to_target