feat(api): origin seed JSON Schema + validator

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/schemas/origin.schema.json

@@ -0,0 +1,52 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://coc-rpg/schemas/origin.schema.json",
+  "title": "Origin Seed",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "schema_version", "id", "display_name", "description",
+    "start_location_id", "situation", "opening_facts",
+    "disposition_overrides", "inventory_grants", "start_quest_id",
+    "build_constraints"
+  ],
+  "properties": {
+    "schema_version": { "type": "integer", "const": 1 },
+    "id": { "type": "string", "pattern": "^[a-z0-9_]+$" },
+    "display_name": { "type": "string", "minLength": 1 },
+    "description": { "type": "string", "minLength": 1 },
+    "start_location_id": { "type": "string", "pattern": "^[a-z0-9_]+$" },
+    "situation": { "type": "array", "items": { "type": "string", "minLength": 1 } },
+    "opening_facts": { "type": "array", "items": { "type": "string", "minLength": 1 } },
+    "disposition_overrides": {
+      "type": "object",
+      "additionalProperties": { "type": "integer", "minimum": -100, "maximum": 100 }
+    },
+    "inventory_grants": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["item_id", "qty"],
+        "properties": {
+          "item_id": { "type": "string", "pattern": "^[a-z0-9_]+$" },
+          "qty": { "type": "integer", "minimum": 1 }
+        }
+      }
+    },
+    "start_quest_id": { "type": ["string", "null"], "pattern": "^[a-z0-9_]+$" },
+    "build_constraints": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["allowed_classes", "luck_modifier"],
+      "properties": {
+        "allowed_classes": {
+          "type": "array",
+          "minItems": 1,
+          "items": { "enum": ["sellsword", "assassin", "priest"] }
+        },
+        "luck_modifier": { "type": "integer" }
+      }
+    }
+  }
+}