fix(oauth): correct OAuth implementation to match bunq documentation

ts/bunq.classes.apicontext.ts

@@ -44,15 +44,6 @@ export class BunqApiContext {
    * Initialize the API context (installation, device, session)
    */
   public async init(): Promise<void> {
-    // If using OAuth token, skip session creation
-    if (this.options.isOAuthToken) {
-      // OAuth tokens already have an associated session
-      this.context.sessionToken = this.options.apiKey;
-      this.session = new BunqSession(this.crypto, this.context);
-      this.session.setOAuthMode(true);
-      return;
-    }
-    
     // Try to load existing context
     const existingContext = await this.loadContext();
     
@@ -78,6 +69,11 @@ export class BunqApiContext {
       this.options.deviceDescription,
       this.options.permittedIps || []
     );
+    
+    // Set OAuth mode if applicable (for session expiry handling)
+    if (this.options.isOAuthToken) {
+      this.session.setOAuthMode(true);
+    }
 
     // Save context
     await this.saveContext();
@@ -135,11 +131,6 @@ export class BunqApiContext {
    * Refresh session if needed
    */
   public async ensureValidSession(): Promise<void> {
-    // OAuth tokens don't need session refresh
-    if (this.options.isOAuthToken) {
-      return;
-    }
-    
     await this.session.refreshSession();
     await this.saveContext();
   }