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/proxy/provider_router.rs

@@ -272,6 +272,7 @@ mod tests {
         dir: TempDir,
         original_home: Option<String>,
         original_userprofile: Option<String>,
+        original_test_home: Option<String>,
     }
 
     impl TempHome {
@@ -279,15 +280,18 @@ mod tests {
             let dir = TempDir::new().expect("failed to create temp home");
             let original_home = env::var("HOME").ok();
             let original_userprofile = env::var("USERPROFILE").ok();
+            let original_test_home = env::var("CC_SWITCH_TEST_HOME").ok();
 
             env::set_var("HOME", dir.path());
             env::set_var("USERPROFILE", dir.path());
+            env::set_var("CC_SWITCH_TEST_HOME", dir.path());
             crate::settings::reload_settings().expect("reload settings");
 
             Self {
                 dir,
                 original_home,
                 original_userprofile,
+                original_test_home,
             }
         }
     }
@@ -303,6 +307,11 @@ mod tests {
                 Some(value) => env::set_var("USERPROFILE", value),
                 None => env::remove_var("USERPROFILE"),
             }
+
+            match &self.original_test_home {
+                Some(value) => env::set_var("CC_SWITCH_TEST_HOME", value),
+                None => env::remove_var("CC_SWITCH_TEST_HOME"),
+            }
         }
     }