test: sync stale fixtures and isolate openclaw env tests

Three unrelated test failures surfaced after rebase:

- McpFormModal expected the apps boolean set without `hermes`; Hermes MCP
  support is now wired, so the fixture must include `hermes: false`.
- therouter Gemini preset was bumped to `gemini-3.1-pro` in a later
  commit; update the assertions to match current config.
- openclaw_config tests mutate process-level `CC_SWITCH_TEST_HOME` and
  `HOME` inside a module-local Mutex, but hermes_config does the same
  under its own separate Mutex. Running both modules in parallel let the
  env races corrupt hermes_config's `with_test_home`. Tag the four
  env-mutating openclaw tests with `#[serial]` so they serialize across
  modules via serial_test's process-wide default key.

src-tauri/src/openclaw_config.rs

@@ -914,6 +914,7 @@ pub fn set_tools_config(tools: &OpenClawToolsConfig) -> Result<OpenClawWriteOutc
 #[cfg(test)]
 mod tests {
     use super::*;
+    use serial_test::serial;
     use std::sync::{Mutex, OnceLock};
 
     fn test_guard() -> std::sync::MutexGuard<'static, ()> {
@@ -966,6 +967,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn default_model_write_preserves_top_level_comments() {
         let source = r#"{
   // top-level comment
@@ -994,6 +996,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn default_model_noop_write_skips_backup() {
         let source = r#"{
   models: {
@@ -1028,6 +1031,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn save_detects_external_conflict() {
         let source = r#"{
   models: {
@@ -1050,6 +1054,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn remove_last_provider_writes_empty_providers_without_panic() {
         let source = r#"{
   models: {