fix(windows): force UTF-8 in channel subprocesses and MCP server env (#345)

Extracted from #318 (the UTF-8/doctor core, minus the env-wrapper feature):

- new agent_reach/utils/process.py: utf8_subprocess_env() +
  mcporter_utf8_env_args() — Windows GBK consoles otherwise corrupt
  Chinese output from mcporter/MCP child processes
- weibo/douyin/linkedin checks and weibo install/registration now pass
  the UTF-8 env (and register the MCP server with --env PYTHONUTF8=1)
- youtube: extract _has_js_runtime_config() with an OSError guard so an
  unreadable yt-dlp config can't crash doctor
- test_skill_command: open SKILL.md with explicit utf-8 (Windows GBK
  default broke these tests)

Co-authored-by: chidao <2980933590@qq.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_skill_command.py

@@ -39,14 +39,11 @@ class TestSkillCommand(unittest.TestCase):
                 with patch.dict(os.environ, env, clear=True):
                     _install_skill()
 
-            target = os.path.join(skill_dir, "agent-reach", "SKILL.md")
             # Check at least one known skill dir pattern
-            found = False
             for dirpath, _, filenames in os.walk(tmpdir):
                 if "SKILL.md" in filenames:
-                    found = True
                     # Verify content is non-empty
-                    with open(os.path.join(dirpath, "SKILL.md")) as f:
+                    with open(os.path.join(dirpath, "SKILL.md"), encoding="utf-8") as f:
                         content = f.read()
                     self.assertIn("Agent Reach", content)
             # _install_skill may or may not find dirs depending on mock; just ensure no crash
@@ -58,7 +55,7 @@ class TestSkillCommand(unittest.TestCase):
             # Create a fake skill installation
             skill_path = os.path.join(tmpdir, ".openclaw", "skills", "agent-reach")
             os.makedirs(skill_path)
-            with open(os.path.join(skill_path, "SKILL.md"), "w") as f:
+            with open(os.path.join(skill_path, "SKILL.md"), "w", encoding="utf-8") as f:
                 f.write("test")
 
             self.assertTrue(os.path.exists(skill_path))
@@ -92,7 +89,7 @@ class TestSkillCommand(unittest.TestCase):
 
             target = os.path.join(skill_parent, "agent-reach", "SKILL.md")
             self.assertTrue(os.path.exists(target))
-            with open(target) as f:
+            with open(target, encoding="utf-8") as f:
                 content = f.read()
             self.assertIn("Agent Reach", content)
 
@@ -114,7 +111,7 @@ class TestSkillCommand(unittest.TestCase):
 
             target = os.path.join(skill_parent, "agent-reach", "SKILL.md")
             self.assertTrue(os.path.exists(target))
-            with open(target) as f:
+            with open(target, encoding="utf-8") as f:
                 content = f.read()
             self.assertTrue(content.strip())
             self.assertIn("WeChat Articles, Xiaoyuzhou Podcast", content)