feat: add FETCH_PRICE permission for manual price fetch endpoint

The POST /api/audit/price-history/fetch endpoint now requires
FETCH_PRICE permission instead of VIEW_AUDIT, which is more
semantically correct since it's a write operation.

backend/models.py

@@ -39,6 +39,7 @@ class Permission(str, PyEnum):
 
     # Audit permissions
     VIEW_AUDIT = "view_audit"
+    FETCH_PRICE = "fetch_price"
 
     # Profile permissions
     MANAGE_OWN_PROFILE = "manage_own_profile"
@@ -84,6 +85,7 @@ ROLE_DEFINITIONS: dict[str, RoleConfig] = {
         "description": "Administrator with audit/invite/appointment access",
         "permissions": [
             Permission.VIEW_AUDIT,
+            Permission.FETCH_PRICE,
             Permission.MANAGE_INVITES,
             Permission.MANAGE_AVAILABILITY,
             Permission.VIEW_ALL_APPOINTMENTS,