Allow AUTH_COOKIE to access @private fields

Add @anoninternal support code

This is a slightly better approach to the previous commit.

server/email: handle errors out of GQL context

server/email: include variables

server: move auth middlware ahead of RealIP

So that @internal auth can correctly test against internal-ipnet.

go fmt

Remove %e formatting verbs

%e is not valid for formatting error values:

> %e	scientific notation, e.g. -1.234456e+78

Instead, use %w when using fmt.Errorf (for error wrapping) and
%v when using log.Printf (%w is not valid in that context).

auth: harden grants structure

This replaces the Access map with a data type whose default value does
not grant any permissions, so that it's more difficult to create an
insecure auth context by mistake.

server: add @private directive glue code

Enforce complexity limit on webhook payload

Configure server to manage mail queue

This also sets up the recovery function for webhooks, so we get emailed
when we panic during a webhook query.

server: add server reference to context

webhooks: initial prototype for GQL-native webhooks

Fix bug with internal authentication

Make authorization errors more specific

server: set max upload size to 1 GiB

Stash remote address in context

Sign outgoing emails

Add legacy webhooks worker implementation

Expand context for work queues