Adds an "/api/whoami" same-origin nginx proxy to authelia's own
GET /api/user/info (session-cookie authenticated, no swarm-controller
code needed) and a new UserMenu header component: a generated initials
avatar (first letter of display name, coloured from the same seven
base16 chromatic slots the nav accent already cycles through) opening a
popover with the signed-in name, a link to authelia settings, and log
out — both reusing the existing "Authelia" entry from GET /api/links
rather than a second source of the domain.
Per mara's call on the open avatar-mechanism question: initials now,
a real uploaded photo (authelia's settings UI implies pics are
settable) is an explicit future item, not blocking this.
dabd0fc823