[Portal] Add Authentication Mode selector for Traditional Web Application

[fungc-io]

Summary

• Add `x_traditional_webapp_session_type` field (`cookie` | `access_token`) to the OAuth client config schema and Go struct
• Add an Authentication Mode radio group on the Traditional Web Application detail page (between Basic Info and URIs); Server-side SDK is shown first and is the default for new apps; Cookie Session is preserved as the default for existing apps that have no value stored
• Add a Select Authentication Mode step in the `/configuration/apps/add` creation wizard, inserted between type selection and save for `traditional_webapp` clients only
• Update the quickstart guide (both the sidebar widget and the post-creation screen) to always show Next.js and Other Framework links for Traditional Web Application clients
• Cookie Session mode shows the Cookie-based authentication section; Server-side SDK mode shows the Refresh Token and Access Token fields
• Inline note shown when switching from Server-side SDK → Cookie Session within an unsaved editing session

ref DEV-3469

🤖 Generated with Claude Code

[tung2744]

Some checks are failing

[fungc-io]

@tung2744 , let's discuss on this change before merging it

[tung2744]

@fungc-io As per latest discussion I think this PR will be closed?

[fungc-io]

Yes, I will redesign and re submit