Standardize D&D prompt asset filenames

assets/dnd/enemy-events/prompts/combat-grounding.md

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+Compact combat grounding is supplied below. It can guide attention and
+disambiguation, but it is not evidence. Do not derive an event, subject,
+outcome, or source range from either list. The current transcript alone must
+directly establish every returned event.
+
+Combat-turn grounding:
+
+{{ input "combat_turns" }}
+
+Named combat-opponent grounding:
+
+{{ input "npc_interactions" }}