feat: add interface-*, cfe-* tests (batches 8+9) — all skills covered

- interface-edit, interface-validate: 2 cases
- cfe-init, cfe-validate, cfe-borrow, cfe-patch-method, cfe-diff: 5 cases
- runner: switch params in preRun (true = no value)
- Findings: interface-edit JSON-in-JSON, cfe-patch-method type naming

52 tests across 40 skills, all passing (~48s).

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

tests/skills/cases/cfe-diff/empty-extension.json

@@ -0,0 +1,10 @@
+{
+  "name": "Diff пустого расширения",
+  "preRun": [
+    {
+      "script": "cfe-init/scripts/cfe-init",
+      "args": { "-Name": "Тест", "-OutputDir": "{workDir}/ext", "-ConfigPath": "{workDir}" }
+    }
+  ],
+  "params": { "extensionPath": "ext" }
+}