Ajoute les extensions et Harmonies : Crescendo

- Format expansions/<bggId>-<nom>/ (expansion.json, rules.fr.json),
  schémas expansion et expansion-rules, guide de contribution
- Harmonies : choix de la face des plateaux personnels (A/B), module
  Esprits de la nature renommé
- Crescendo (472690) : modules Sanctuaires et Murmures, faces C et D,
  fiche de règles résumée

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

schemas/expansion-rules.schema.json

@@ -0,0 +1,60 @@
+{
+  "type": "object",
+  "properties": {
+    "$schema": {
+      "type": "string"
+    },
+    "schemaVersion": {
+      "type": "number",
+      "const": 1
+    },
+    "locale": {
+      "type": "string",
+      "enum": [
+        "fr"
+      ],
+      "default": "fr"
+    },
+    "summary": {
+      "type": "string",
+      "maxLength": 300,
+      "minLength": 1
+    },
+    "goal": {
+      "type": "string",
+      "maxLength": 1000
+    },
+    "setup": {
+      "type": "string",
+      "maxLength": 3000
+    },
+    "turn": {
+      "type": "string",
+      "maxLength": 5000
+    },
+    "end": {
+      "type": "string",
+      "maxLength": 2000
+    },
+    "scoring": {
+      "type": "string",
+      "maxLength": 3000
+    },
+    "tips": {
+      "type": "string",
+      "maxLength": 2000
+    },
+    "officialRulesUrl": {
+      "type": "string",
+      "format": "uri",
+      "pattern": "^https\\:\\/\\/"
+    }
+  },
+  "required": [
+    "schemaVersion",
+    "summary"
+  ],
+  "additionalProperties": false,
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Fiche de règles d'une extension (rules.fr.json)"
+}