Add D&D NPC extraction and validation

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

@@ -0,0 +1,16 @@
+Extract a concise Dungeons & Dragons non-player-character registry from the
+provided transcript.
+
+Include an in-world non-PC participant when the transcript establishes that it
+appears, acts, speaks, or is materially discussed and gives it a proper name,
+a stable alias or title, or an individually useful distinguishing description.
+
+Exclude human players, transcript speakers, the GM as an out-of-world person,
+player characters identified by the player or party references, incidental or
+hypothetical name drops, corrected transcription mistakes, characters mentioned
+only by reference material, indistinguishable crowds or groups, and temporary
+summoned creatures or spell effects without a persistent individual identity.
+
+Return canonical in-world names rather than player names or transcript speaker
+names. Keep each description concise and limited to facts established by the
+transcript. Include only explicitly supported aliases and relationships.