refactor: consolidate legacy record_turn_memory into unified API (T90.3)

The Phase 1 single-bot ``record_turn_memory`` lingered next to the
unified ``record_turn_memory_for_present`` introduced in T84. Only test
fixtures still called the legacy entry point.

- Remove ``record_turn_memory`` from ``chat/services/memory_write.py``.
- Update the two test_memory_write.py callers to use
  ``record_turn_memory_for_present(..., guest_bot_id=None)``, which
  produces the same ``[you=1, host=1, guest=0]`` witness mask.

The unified API returns ``dict[bot_id, (event_id, memory_id)]``; tests
extract the host entry. No production callers were affected.

tests/test_memory_write.py

@@ -22,7 +22,7 @@ from chat.db.migrate import apply_migrations
 from chat.eventlog.log import append_event
 from chat.eventlog.projector import project
 from chat.llm.mock import MockLLMClient
-from chat.services.memory_write import record_turn_memory, record_turn_memory_for_present
+from chat.services.memory_write import record_turn_memory_for_present
 import chat.state.entities  # noqa: F401  - register handlers
 import chat.state.memory  # noqa: F401
 import chat.state.world  # noqa: F401
@@ -64,14 +64,19 @@ def test_record_turn_memory_writes_event_and_projects(tmp_path):
     apply_migrations(db)
     _seed_minimal(db)
     with open_db(db) as conn:
-        eid, mid = record_turn_memory(
+        # T90.3: legacy ``record_turn_memory`` was removed; the unified
+        # ``record_turn_memory_for_present`` with ``guest_bot_id=None``
+        # produces the same single-bot witness mask [1,1,0].
+        result = record_turn_memory_for_present(
             conn,
             chat_id="chat_bot_a",
             host_bot_id="bot_a",
+            guest_bot_id=None,
             narrative_text="BotA looks up. 'You're back late.'",
             scene_id=None,
             chat_clock_at="2026-04-26T20:00:00+00:00",
         )
+        eid, mid = result["bot_a"]
         assert eid > 0
         assert mid is not None and mid > 0
 
@@ -111,12 +116,15 @@ def test_record_turn_memory_omits_optional_fields(tmp_path):
     _seed_minimal(db)
     with open_db(db) as conn:
         # Call without scene_id/chat_clock_at — should default to None.
-        eid, mid = record_turn_memory(
+        # T90.3: migrated from legacy ``record_turn_memory``.
+        result = record_turn_memory_for_present(
             conn,
             chat_id="chat_bot_a",
             host_bot_id="bot_a",
+            guest_bot_id=None,
             narrative_text="A simple memory.",
         )
+        eid, mid = result["bot_a"]
         assert eid > 0
         assert mid is not None and mid > 0