Move D&D spell assets into extractor module

internal/modules/extract/dnd/spells/assets/prompts/system.md

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+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/modules/extract/dnd/spells/assets/prompts/user.md

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+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.

internal/modules/extract/dnd/spells/assets/schemas/dnd_spells.v1.json

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+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "notarius.dnd.spells",
+  "type": "object",
+  "additionalProperties": false,
+  "required": ["spell_casts"],
+  "properties": {
+    "spell_casts": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": [
+          "caster",
+          "spell",
+          "effect",
+          "narrative_description",
+          "source_refs"
+        ],
+        "properties": {
+          "caster": {
+            "type": "string",
+            "minLength": 1
+          },
+          "spell": {
+            "type": "string",
+            "minLength": 1
+          },
+          "effect": {
+            "type": "string",
+            "minLength": 1
+          },
+          "narrative_description": {
+            "type": "string",
+            "minLength": 1
+          },
+          "source_refs": {
+            "type": "array",
+            "minItems": 1,
+            "items": {
+              "type": "object",
+              "additionalProperties": false,
+              "required": ["source_id", "start_unit_id", "end_unit_id"],
+              "properties": {
+                "source_id": {
+                  "type": "string",
+                  "minLength": 1
+                },
+                "start_unit_id": {
+                  "type": "string",
+                  "minLength": 1
+                },
+                "end_unit_id": {
+                  "type": "string",
+                  "minLength": 1
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}