fix(test): resolve HOME env race condition in parallel tests

- Use get_home_dir() instead of dirs::home_dir() in get_opencode_dir()
  and get_openclaw_dir() to respect CC_SWITCH_TEST_HOME override
- Add CC_SWITCH_TEST_HOME to all TempHome implementations
- Add #[serial] to all with_test_home tests to share serialization
  with other env-mutating tests
- Remove --test-threads=1 workaround from CI

src-tauri/src/opencode_config.rs

@@ -37,9 +37,9 @@ pub fn get_opencode_dir() -> PathBuf {
         return override_dir;
     }
 
-    dirs::home_dir()
-        .map(|h| h.join(".config").join("opencode"))
-        .unwrap_or_else(|| PathBuf::from(".config").join("opencode"))
+    crate::config::get_home_dir()
+        .join(".config")
+        .join("opencode")
 }
 
 pub fn get_opencode_config_path() -> PathBuf {