Add grounded NPC interaction extractor

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

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+Return the interactions array even when no interaction is established. Every
+record must contain name, kind, and source_refs. Cite transcript ranges that
+support both the NPC identity and the interaction kind.
+
+Use exactly one kind per occurrence:
+
+- mentioned: the NPC is referred to but is not established as present or communicating;
+- noncombat_presence: the NPC is present and relevant but does not meaningfully participate in dialogue or combat;
+- dialogue: the NPC speaks, responds, or is directly engaged in a meaningful non-combat exchange;
+- combat_ally: the NPC actively participates in combat on the party's side;
+- combat_opponent: the NPC actively participates in combat against the party; or
+- other: the transcript clearly establishes a direct NPC occurrence that fits none of the preceding kinds.
+
+When activities overlap, active combat participation outranks dialogue,
+presence, and mention; dialogue outranks noncombat presence and mention; and
+noncombat presence outranks mention. Other is only for directly evidenced
+activity outside those categories. Split an occurrence rather than assigning
+both combat alignments.