Record batch runs beside cascades so Home lists them

A batch run opens no cascade, and FlowRun was written only from
cascade_started — so `fluksio run` showed on /runs and in `fluksio status` and
was simply absent from Home. The collector now folds the run_started and
run_finished events RunService already published. Such a record is exempt from
the staleness sweep in both places: a training step of an hour is a normal one,
and only run_finished ends it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backend/fluksio/models.py

@@ -279,14 +279,19 @@ class EngineEvent(SQLModel, table=True):
 
 
 class FlowRun(SQLModel, table=True):
-    """One cascade, from the item that started it to the last node in it."""
+    """One cascade, from the item that started it to the last node in it.
+
+    Or one batch run: it opens no cascade, but it is still a thing that ran,
+    and the history screens are where somebody looks for it.
+    """
 
     __tablename__ = "flow_run"
 
-    #: The queue entry id, or a `manual-` one for a run that never queued.
+    #: The queue entry id, a `manual-` one for a run that never queued, or the
+    #: `Run.id` of a batch run.
     id: str = Field(primary_key=True, max_length=64)
     flow: str = Field(index=True, max_length=255)
-    #: What caused it: the work item's cause, or "manual".
+    #: What caused it: the work item's cause, "manual", or "run" for a batch.
     source: str = ""
     started_at: datetime = Field(
         index=True,
@@ -296,7 +301,7 @@ class FlowRun(SQLModel, table=True):
         default=None,
         sa_type=UTCDateTime,
     )
-    #: running, ok, error or abandoned.
+    #: running, ok, error, abandoned — or whatever a batch run ended as.
     status: str = "running"
     nodes: int = 0
     errors: int = 0