feat(eval): server-side replay/phase1 timing + memoir phase1 batch chunking

- Replay and memoir-submit responses include started/finished UTC and elapsed_ms;
  Phase1 poll exposes Redis-backed submit time and elapsed_ms_since_submit.
- Phase1 batch LLM splits segments by memoir_phase1_batch_llm_chunk_size with
  bisect fallback per chunk; Playground shows server timings.

Made-with: Cursor

api/tests/test_memoir_pipeline_optimization.py

@@ -30,6 +30,7 @@ def test_phase1_batch_enabled_by_default() -> None:
 
     s = Settings()
     assert s.memoir_phase1_batch_llm_enabled is True
+    assert s.memoir_phase1_batch_llm_chunk_size >= 1
 
 
 def test_quality_pass_enabled_by_default() -> None: