Self-hosted desktop SSO (#5265)

# Description of Changes
Support SSO in self-hosted desktop app.

---------

Co-authored-by: Anthony Stirling <[email protected]>

frontend/src/proprietary/extensions/accountLogout.ts

@@ -0,0 +1,20 @@
+type SignOutFn = () => Promise<void>;
+
+interface AccountLogoutDeps {
+  signOut: SignOutFn;
+  redirectToLogin: () => void;
+}
+
+/**
+ * Default (web/proprietary) logout handler: sign out and redirect to /login.
+ * Desktop builds override this file via path resolution.
+ */
+export function useAccountLogout() {
+  return async ({ signOut, redirectToLogin }: AccountLogoutDeps): Promise<void> => {
+    try {
+      await signOut();
+    } finally {
+      redirectToLogin();
+    }
+  };
+}

frontend/src/proprietary/extensions/authCallback.ts

@@ -0,0 +1,7 @@
+/**
+ * Extension hook for platform-specific OAuth callback handling.
+ * Proprietary/web builds are no-op.
+ */
+export async function handleAuthCallbackSuccess(_token: string): Promise<void> {
+  // no-op for web builds
+}

frontend/src/proprietary/extensions/authSessionCleanup.ts

@@ -0,0 +1,11 @@
+/**
+ * Extension hooks for platform-specific auth cleanup.
+ * Proprietary/web builds are no-op.
+ */
+export async function clearPlatformAuthAfterSignOut(): Promise<void> {
+  // no-op for web builds
+}
+
+export async function clearPlatformAuthOnLoginInit(): Promise<void> {
+  // no-op for web builds
+}

frontend/src/proprietary/extensions/oauthNavigation.ts

@@ -0,0 +1,7 @@
+/**
+ * Extension hook for platform-specific OAuth navigation.
+ * Proprietary/web builds default to in-window navigation.
+ */
+export async function startOAuthNavigation(_redirectUrl: string): Promise<boolean> {
+  return false;
+}