Allow bool web_search in ToolsToml (#14352)

Summary
- add a custom deserializer so `[tools].web_search` can be a bool
(treated as disabled) or a config object
- extend core and app-server tests to cover bool handling in TOML config

Testing
- Not run (not requested)

codex-rs/core/src/config/config_tests.rs

@@ -175,6 +175,44 @@ enabled = false
     );
 }
 
+#[test]
+fn tools_web_search_true_deserializes_to_none() {
+    let cfg: ConfigToml = toml::from_str(
+        r#"
+[tools]
+web_search = true
+"#,
+    )
+    .expect("TOML deserialization should succeed");
+
+    assert_eq!(
+        cfg.tools,
+        Some(ToolsToml {
+            web_search: None,
+            view_image: None,
+        })
+    );
+}
+
+#[test]
+fn tools_web_search_false_deserializes_to_none() {
+    let cfg: ConfigToml = toml::from_str(
+        r#"
+[tools]
+web_search = false
+"#,
+    )
+    .expect("TOML deserialization should succeed");
+
+    assert_eq!(
+        cfg.tools,
+        Some(ToolsToml {
+            web_search: None,
+            view_image: None,
+        })
+    );
+}
+
 #[test]
 fn config_toml_deserializes_model_availability_nux() {
     let toml = r#"