Improved Auth Flow

We need effectively two flows that are going to reuse the upstream Sentry OAuth consumption:

1. MCP-initiated, with the cloudflare oauth proxy and dynamic client registration
2. Self-initiated, allowing us to get your userId and bind it in a local web session

This allows us to associate all data within a durable object on the user's ID attribute. That object will contain a few concerns:

- a list of client IDs (MCP clients effectively)
- a default organization per client ID

Around (1) this will be auto populated and/or populated via an intermediate step as defined in #1.

For (2) this will give you effectively a "settings" screen (#3), which should also allow you to revoke an upstream token (unclear if thats possible yet today) - see also #2.