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.