Render an Apple configuration profile from the server's PACC document

iOS is the one client none of the mail autoconfiguration reaches: Apple
Mail reads neither Mozilla autoconfig nor Autodiscover for IMAP, so
adding an account means the device probing for ports - and a probe that
meets a filtered port waits out a TCP timeout and reports the account as
unverifiable, which the person reads as a wrong password.

A profile states the hosts and the ports instead, and carries mail,
calendars and contacts in one install. It invents none of them: site.yaml
names a PACC document - the standard defined to be fetched from the mail
domain itself - and every host, port and collection path comes from
there, so the server is described in one place and the profile follows it.

The document holds no address, username or password. iOS asks for those
at install, which means one profile serves everyone with an account and
it can be fetched by anyone: it says no more than PACC already says in
public. Identifiers are derived from the site and the payload rather than
drawn at random, because iOS replaces a profile whose ids it knows and
stacks a duplicate when they differ.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015GeH3y8fwTaTudaD88P57o

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "portal"
-version = "0.6.21"
+version = "0.6.22"
 edition = "2021"
 
 [lib]