better-auth AT Protocol (Bluesky) Plugin

This package provides an AT Protocol (Bluesky) OAuth plugin for the `better-auth` framework. It enables users to sign in with their Bluesky or any AT Protocol Personal Data Server (PDS) account, leveraging OAuth 2.0 with PKCE and DPoP for secure authentication. Currently at version 0.1.0 (initial release), its release cadence is expected to be event-driven as a new, specialized plugin. Key differentiators include built-in support for localhost development without tunnels via AT Protocol's loopback client, automatic hosting of necessary OAuth discovery endpoints (`client-metadata.json` and `jwks.json`), and persistence of OAuth state and session data through `better-auth`'s database adapter. It also features automatic profile synchronization, updating user details like DID, handle, and display name.