A run says whether the dashboard, the CLI or a script asked for it

`POST /runs/flows/{name}` hardcoded `cause: "api"`, so every row in the
history claimed the same origin. The body now carries an optional `cause`,
closed to the values the column knows — the dashboard sends nothing and stays
"api", `fluksio run` says "cli", and the SDK client says "sdk".

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Gf7WaExcJ9bs3kfJXB3nK

backend/fluksio/models.py

@@ -340,7 +340,7 @@ class Run(SQLModel, table=True):
     group_id: str | None = Field(default=None, index=True, max_length=64)
     #: The run this one was made from, on a retry.
     parent_id: str | None = Field(default=None, max_length=64)
-    #: api, hook, sweep or cli.
+    #: Where it was asked for: api, cli, sdk, hook or sweep.
     cause: str = Field(default="api", max_length=32)
     #: Re-execute every node, whatever the stage cache holds for it.
     no_cache: bool = False