feat(playground): project selector with auto token loading

[carlosatta]

Feature Request

Proposed by @EdisAganovic in #36 (comment)

Description

In the playground, allow the user to select a project from a dropdown. Once selected, the corresponding API token should be loaded automatically in the background (without being visible), so the user can test immediately without manually copying and pasting the token.

Motivation

Currently the user has to:

1. Go to the project settings to find/copy the token
2. Paste it manually in the playground

This is especially cumbersome when running Routerly self-hosted over HTTP (Docker via IP), where the clipboard API is blocked.

Proposed UX

• Add a project selector (dropdown) at the top of the playground
• When a project is selected, its token is loaded silently in the request headers
• The token value is not shown to the user in the UI

Status

Under discussion — needs evaluation before implementation.

[carlosatta]

The playground is designed to test the full chain end-to-end, authentication included. A couple of problems worth discussing before moving forward.

1. Security
Auto-loading a token in the background raises an important question: where does the FE get it? If the FE holds the token, that's a security concern. The alternative (having the BE proxy the call on behalf of the selected project) would avoid exposing the token to the client, but it adds significant complexity and breaks the core purpose of the playground: testing the real call chain, auth included.

2. Granularity
A project can have multiple tokens (different names/scopes). The selector would need to be two-level: project -> token, not just project.

Both points need to be addressed before deciding whether and how to implement this.