Flow inputs carry an origin hint, run or panel

The Inputs editor and the canvas label show it, and the run forms leave
panel inputs out.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx

backend/fluksio/flow/schemas.py

@@ -267,6 +267,15 @@ class FlowInput(BaseModel):
 
     spec: MessageSpec
     initial: Any | None = None
+    origin: Literal["run", "panel"] = Field(
+        default="run",
+        description=(
+            "What writes it. A run input is a parameter a run passes in, a "
+            "panel input is written by a dashboard or panel control. A hint "
+            "only: run forms leave panel inputs out, the engine treats both "
+            "the same."
+        ),
+    )
 
 
 class FlowDef(BaseModel):