panel: match monitoring URLs to their nav labels

/sendlog -> /deliveries, /queue -> /mail-queue, /logtail -> /system-log,
along with the HTMX polling fragments under each.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

internal/web/templates/logtail_body.html

@@ -1,5 +1,5 @@
 {{define "logtail_body"}}
-<div id="logtail-body" hx-get="/logtail/body" hx-trigger="every 5s" hx-swap="outerHTML">
+<div id="logtail-body" hx-get="/system-log/body" hx-trigger="every 5s" hx-swap="outerHTML">
   {{if .Error}}<p class="error">{{.Error}}</p>{{end}}
   <span class="code">{{if .Lines}}{{range .Lines}}{{.}}
 {{end}}{{else}}No log lines yet.{{end}}</span>