Bug 1 (secondary): _persist_pre() created TranslationLanguage with
empty final_value for non-source target languages when same_language
flag was set but no cache/approved value existed. This produced
is_original=0 rows with empty text in target table.
Fix: skip TranslationLanguage creation when fv is empty (continue
in the loop instead of falling through to else with empty string).
Bug 2 (diagnostic): No visibility into _classify() routing decisions.
Add logger.reason with pre/llm/total counts per batch.
Scenario trace: ru source + targets [ru,en] + no cache → llm_rows ✓
If same-language partial match hits cache for all targets → pre_rows ✓
If same-language partial match misses cache → llm_rows ✓
If same-language all-match (targets=[ru]) → short-circuit pre_rows ✓
Tests: 69/69 translate tests pass.