feat: add cf-init test cases, support args_extra and params priority

- cf-init: 3 cases (basic, with-vendor, error-already-exists)
- runner: args_extra for optional CLI params per case
- runner: params.field takes priority over caseData.field in case.<field> mapping

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/skills/cases/cf-init/basic.json

@@ -0,0 +1,7 @@
+{
+  "name": "Пустая конфигурация",
+  "params": { "name": "ТестоваяКонфигурация" },
+  "expect": {
+    "files": ["Configuration.xml", "Languages/Русский.xml"]
+  }
+}