Load app-server config through ConfigManager (#18870)

## Summary
- Load app-server startup config through `ConfigManager` instead of
direct `ConfigBuilder` calls.
- Move `ConfigManager` constructor-owned state (`cli_overrides`, runtime
feature map, cloud requirements loader) behind internal manager fields.
- Pass `ConfigManager` into `MessageProcessor` directly instead of
reconstructing it from raw args.

## Tests
- `cargo check -p codex-app-server`
- `cargo test -p codex-app-server`
- `just fix -p codex-app-server`
- `just fmt`

codex-rs/app-server/src/message_processor.rs

@@ -1,9 +1,7 @@
-use std::collections::BTreeMap;
 use std::collections::HashSet;
 use std::future::Future;
 use std::sync::Arc;
 use std::sync::OnceLock;
-use std::sync::RwLock;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::Ordering;
 
@@ -64,11 +62,8 @@ use codex_app_server_protocol::ServerRequestPayload;
 use codex_app_server_protocol::experimental_required_message;
 use codex_arg0::Arg0DispatchPaths;
 use codex_chatgpt::connectors;
-use codex_config::ThreadConfigLoader;
 use codex_core::ThreadManager;
 use codex_core::config::Config;
-use codex_core::config_loader::CloudRequirementsLoader;
-use codex_core::config_loader::LoaderOverrides;
 use codex_exec_server::EnvironmentManager;
 use codex_features::Feature;
 use codex_feedback::CodexFeedback;
@@ -92,7 +87,6 @@ use tokio::sync::broadcast;
 use tokio::sync::watch;
 use tokio::time::Duration;
 use tokio::time::timeout;
-use toml::Value as TomlValue;
 use tracing::Instrument;
 
 const EXTERNAL_AUTH_REFRESH_TIMEOUT: Duration = Duration::from_secs(10);
@@ -233,11 +227,8 @@ pub(crate) struct MessageProcessorArgs {
     pub(crate) outgoing: Arc<OutgoingMessageSender>,
     pub(crate) arg0_paths: Arg0DispatchPaths,
     pub(crate) config: Arc<Config>,
+    pub(crate) config_manager: ConfigManager,
     pub(crate) environment_manager: Arc<EnvironmentManager>,
-    pub(crate) cli_overrides: Vec<(String, TomlValue)>,
-    pub(crate) loader_overrides: LoaderOverrides,
-    pub(crate) cloud_requirements: CloudRequirementsLoader,
-    pub(crate) thread_config_loader: Arc<dyn ThreadConfigLoader>,
     pub(crate) feedback: CodexFeedback,
     pub(crate) log_db: Option<LogDbLayer>,
     pub(crate) config_warnings: Vec<ConfigWarningNotification>,
@@ -255,11 +246,8 @@ impl MessageProcessor {
             outgoing,
             arg0_paths,
             config,
+            config_manager,
             environment_manager,
-            cli_overrides,
-            loader_overrides,
-            cloud_requirements,
-            thread_config_loader,
             feedback,
             log_db,
             config_warnings,
@@ -292,18 +280,6 @@ impl MessageProcessor {
             .plugins_manager()
             .set_analytics_events_client(analytics_events_client.clone());
 
-        let cli_overrides = Arc::new(RwLock::new(cli_overrides));
-        let runtime_feature_enablement = Arc::new(RwLock::new(BTreeMap::new()));
-        let cloud_requirements = Arc::new(RwLock::new(cloud_requirements));
-        let config_manager = ConfigManager::new(
-            config.codex_home.to_path_buf(),
-            cli_overrides,
-            runtime_feature_enablement,
-            loader_overrides,
-            cloud_requirements,
-            arg0_paths.clone(),
-            thread_config_loader,
-        );
         let codex_message_processor = CodexMessageProcessor::new(CodexMessageProcessorArgs {
             auth_manager: auth_manager.clone(),
             thread_manager: Arc::clone(&thread_manager),