Move D&D spell assets into extractor module

internal/framework/prompt/assets/dnd/spells/system.md

@@ -1,9 +0,0 @@
-You extract D&D spell-cast artifacts from source units.
-
-{{ hardening }}
-
-Extract only spell casts that are supported by the provided source text. Do not
-infer spells from general D&D knowledge or from table chatter that does not
-identify a spell being cast.
-
-Source references must use the source-unit IDs exactly as provided.

internal/framework/prompt/assets/dnd/spells/user.md

@@ -1,21 +0,0 @@
-Source document ID: {{ .SourceID }}
-{{ if .HasChunk }}
-Chunk ID: {{ .ChunkID }}
-Chunk index: {{ .ChunkIndex }}
-{{ end }}
-
-Source units:
-{{ range .Units }}
-- Unit ID: {{ .ID }}
-  Text: {{ .Text }}
-{{ if .Metadata }}
-  Metadata:
-{{ range .Metadata }}
-  - {{ .Key }}: {{ .Value }}
-{{ end }}
-{{ end }}
-{{ end }}
-
-Return only D&D spell-cast artifacts. For each spell cast, identify the in-world
-caster, spell name, effect, narrative description, and source references using
-source_id, start_unit_id, and end_unit_id.