Add combat semantics validator prompt assets

assets/dnd/scene-descriptions/validate/combat-semantics/prompts/instructions.md

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+Review only whether the proposed scene kind correctly represents substantive
+active combat in the supplied transcript chunk under the shared combat policy.
+Do not judge the scene title, summary, non-combat subtype, scene boundary, or
+any other aspect of a scene description.
+
+Return `approved` only when the proposed kind's combat status is supported;
+approval does not endorse any other part of the scene description. Return
+`combat_should_be_added` when a proposed non-combat kind omits substantive
+active combat. Return `combat_should_be_removed` when a proposed `combat` kind
+is unsupported. Give a concise, transcript-grounded explanation for every
+verdict.