Add SPC convective outlook data contracts

docs/internal/facts.md

@@ -20,7 +20,8 @@ Inputs:
 Outputs:
 
 - `facts.CollectedFacts` with normalized source facts plus separate source
-  provenance and warnings
+  provenance and warnings. SPC convective outlook source data is carried
+  through when present in the bundle.
 - `facts.DerivedFacts` with valid-period forecast slices, alert overlaps,
   daily summaries, daypart summaries, and Storm Report window summary
 
@@ -55,6 +56,7 @@ and inspection.
   derivation error for reports that require daily summaries.
 - Missing optional narrative, alert, discussion, daily, or weather story data
   produces empty or nil derived fields.
+- Missing optional SPC convective outlook data produces a nil collected field.
 
 ## Tests