feat: account menu, database roles, and single logout

Bundles the console work from the current branch: the header account
control, database-backed roles and permissions, and signing out across
the applications that share this sign-in.

The account control replaces a separate identity chip and a separate
sign-out button, which meant the header carried two controls describing
one fact. web/account.js is mounted into every page by a placeholder and
owns the keyboard handling, the outside-click behaviour and the sign-out
form once. It also fills the trigger's name, which the previous markup
left empty.

Signing out revokes the hosted-login bearer sessions this installation
issued, then redirects to the provider's end_session_endpoint when the
discovery document advertises one. Applications that authenticate
against this installation therefore lose their session too; one pointed
straight at an identity provider is out of its reach and is unchanged.

Roles and permissions become rows rather than a closed enum, so a tenant
can extend the catalog without a migration, and a role can no longer be
granted a capability that is not in it. requireSameOrigin now compares
against the origin the request arrived on instead of the configured base
URL, which defaulted to http://localhost:8080 and so rejected every
write in a deployment that never set it.

Two bugs found while verifying in a browser:

  - A profile picture never rendered. avatarURL built an absolute URL
    from the configured base URL, and the page's own img-src 'self'
    blocked it. The console's own pages now take a root-relative path;
    only /connect/userinfo, read from another origin, needs an absolute
    one, and it follows the request.
  - absoluteURL preferred the configuration over the request while its
    comment claimed the opposite, which also misdirected the logout
    redirect.

Card layout: the footer was one two-column row shared between a label
and a forty-character identifier, so the identifier took the width and
crushed its label into three stacked words. Each pair is a line now, the
value truncates with the full text in the title, and cards align their
footers across a row.

internal/server/useradmin.go

@@ -89,7 +89,7 @@ func (s *Server) inviteUser(w http.ResponseWriter, r *http.Request) {
 		s.handleStoreError(w, "invite user", err)
 		return
 	}
-	user.AvatarURL = s.avatarURL(user.AvatarKey)
+	user.AvatarURL = s.avatarPath(user.AvatarKey)
 	writeJSON(w, http.StatusCreated, user)
 }