docs: the three services, their versions and traces (#207, #213)

architecture.md opens on the three services, how a trace crosses them, and the directory's
modules; sso.md's diagram and config show ipx-web in front, trusting Caddy and passing headers
only from TUNNEL_PEER; configuration.md has ipx-web's variables and the Directory as the
service's; cli.md and users.md stop describing the old local Directory; directory.md has its
traces and version.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/directory.md

@@ -71,6 +71,13 @@ token_sha256 = "…"
 `DIRECTORY_LOG_FORMAT=json` logs one JSON object a line, for Loki, as ipx's `IPX_LOG_FORMAT` does.
 Each request is a line with its `method`, `path`, `status`, `duration_ms` and the `token`'s name.
 
+With `OTEL_EXPORTER_OTLP_ENDPOINT` set (`http://host:4318`, OTLP over HTTP), it sends traces: a
+span a request, a child of the caller's when the request carries a `traceparent`, as ipx's do, and
+a trace a refresher round with a span a feed (#213). `OTEL_RESOURCE_ATTRIBUTES` tags them, as
+production does with `deployment.environment.name=production`. Its version is in
+`crates/directory/Cargo.toml`, logged at start and answered by `ipx-directory --version`; its
+changelog is `crates/directory/CHANGELOG.md`.
+
 ## Running one
 
 ```yaml