Add standalone D&D combat turn extraction

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

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+Return exactly one JSON object and no explanatory text.
+
+Return the combat_turns array even when no combat turn is established. Return
+one or more actions for every turn. Use one of the supported turn_kind and
+action category values. Set round to null when the transcript does not state
+an explicit or unambiguous positive round number. Set resolution to null when
+the transcript establishes the declaration but not an immediate resolution.
+
+Every source reference must contain start_unit_id and end_unit_id from the
+provided transcript. Do not add source_id; the extraction mapper assigns the
+current source identity. Do not include fields not defined by the response
+schema.