Add grounded NPC interaction extractor

internal/modules/dnd/extract/npcinteractions/assets/prompts/task.md

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+Extract Dungeons & Dragons NPC interaction occurrences from the supplied
+transcript.
+
+Include an occurrence only when the transcript establishes one supplied NPC,
+one interaction kind, and a coherent passage supporting both. Use only names
+from the supplied NPC registry. The registry helps ground identity but never
+proves that an interaction occurred.
+
+Do not summarize, infer relationships, sentiment, factions, motives, aliases,
+or persistent state. Do not identify player characters, anonymous groups, or
+invented NPCs. Return an empty interactions array when no supplied NPC has an
+evidenced interaction in this transcript passage.
+
+Keep occurrences within this transcript chunk. Split records when an NPC's
+interaction kind changes, when combat alignment changes, or when an NPC is
+first mentioned and later becomes present.