fix(optimal): make IndexJournalEntryParams.entry_id required

Task 22 added a runtime ValueError when entry_id is None, but the
dataclass still typed it Optional. Contract-vs-runtime split — callers
get no IDE/mypy hint about the required field. Tighten the type to
UUID (required) and remove the misleading "can be None for system
events" docstring note. Lifecycle events already use their synthetic
uuid5 path, so no real caller is broken.

tests/unit/services/test_optimal_doc_source.py

@@ -75,18 +75,25 @@ async def test_index_journal_entry_raises_when_entry_id_is_none() -> None:
     """``entry_id=None`` must raise — the silent fallback hid an upstream
     bug where the entry row hadn't been flushed before indexing, producing
     ``roboco://journals/None`` doc-sources in the RAG store.
+
+    ``entry_id`` is typed ``UUID`` (required); a real caller would have to
+    bypass the dataclass type contract for this to fire (e.g. via
+    ``cast(UUID, None)``). We simulate that with a ``SimpleNamespace`` so
+    we don't have to reach inside a frozen-style dataclass to clobber a
+    field — same pattern used by the conversation test below.
     """
     svc = _service_with_stub_plugin()
-    params = IndexJournalEntryParams(
+    fake_params = SimpleNamespace(
         content="some reflection",
         entry_type="reflect",
         entry_id=None,  # the bug we now reject
         agent_id=uuid4(),
         task_id=uuid4(),
+        tags=None,
     )
 
     with pytest.raises(ValueError, match="entry_id is required"):
-        await svc.index_journal_entry(params)
+        await svc.index_journal_entry(cast("IndexJournalEntryParams", fake_params))
 
 
 @pytest.mark.asyncio