refactor(config): unify secrets in ~/.mytoolkit/config.json and migrate skill wrappers

tests/conftest.py

@@ -9,3 +9,4 @@ import os
 import tempfile
 
 os.environ["MYTOOLKIT_HOME"] = tempfile.mkdtemp(prefix="mytoolkit-test-home-")
+os.environ["MYTOOLKIT_NO_EXTERNAL_MIGRATION"] = "1"

tests/test_config.py

@@ -77,6 +77,6 @@ def test_legacy_env_merges_without_clobbering_existing_keys(fresh_home):
         json.dumps({"vars": {"apikey_ark": "sk-old", "extra": "e"}})
     )
     c = Config()
-    # Legacy vars are merged in (documented behaviour: legacy wins on conflict).
+    # Unknown legacy vars are merged in; known keys keep the existing mytoolkit value.
     assert c.get("extra") == "e"
-    assert c.get("apikey_ark") == "sk-old"
+    assert c.get("apikey_ark") == "sk-new"