User guide

Each guide covers one role or task and links to the API reference on pkg.go.dev rather than repeating it.

Guide	Read it to
How AAuth works	Learn the roles, tokens, and system shapes before reading any code
Flows	See a sequence diagram of each exchange: tokens, consent, four-party, missions, chaining, revocation
Getting started	Install the module, see which drafts it implements, and pick a package
Agent	Sign requests, obtain tokens through Transport, and use missions and permissions
Resource	Verify tokens and challenge for the next one
Hosted AP, PS, and AS	Run the agent provider, Person Server, and Access Server roles
Design and security notes	Understand the library's boundaries and operational cautions
Testing	Run the tests, examples, and conformance vectors
Migrating from v0.1	Upgrade to the draft -11 wire format