[profile-switcher][rust] -- [1/2] Add app-server account session protocol (#25469)

## Summary

Adds the app-server v2 `accountSession/*` protocol used by the Desktop
profile switcher and the backend account metadata client needed to
populate workspace choices.

This is the protocol layer only. The app-server lifecycle and
consolidated saved-session storage are split into a follow-up PR.

## Rust Stack

1. This PR
2. [openai/codex#25383](https://github.com/openai/codex/pull/25383) adds
app-server session lifecycle behavior and consolidated saved-session
storage.

## Validation

- Generated app-server schema fixtures are included from the existing
generation flow in the lifecycle PR where the routes are registered.
- Did not run tests per requested scope.

codex-rs/app-server-protocol/src/protocol/v2/account.rs

@@ -138,6 +138,78 @@ pub struct CancelLoginAccountResponse {
     pub status: CancelLoginAccountStatus,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionsAddParams {
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub switch_to_added_account: bool,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionsListParams {
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub refresh_workspace_metadata: bool,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionsLogoutParams {
+    pub session_id: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionsSwitchParams {
+    pub session_id: String,
+    pub account_id: String,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionsResponse {
+    pub active_session_id: Option<String>,
+    pub sessions: Vec<AccountSession>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSession {
+    pub session_id: String,
+    pub email: Option<String>,
+    pub user_id: Option<String>,
+    pub display_name: Option<String>,
+    pub image_url: Option<String>,
+    pub last_used_at: i64,
+    pub is_active: bool,
+    pub selected_workspace_account_id: Option<String>,
+    pub workspaces: Vec<AccountSessionWorkspace>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct AccountSessionWorkspace {
+    pub account_id: String,
+    pub name: Option<String>,
+    pub image_url: Option<String>,
+    pub kind: Option<AccountSessionWorkspaceKind>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub enum AccountSessionWorkspaceKind {
+    Personal,
+    Workspace,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]