Split internal/web into subpackages before domain-admin growth.

Lay out view, auth, validate, and handlers under internal/web while keeping
the cmd/panel API unchanged; update roadmap and changelog for web-split closure.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/view/templates/system_log.html

@@ -0,0 +1,12 @@
+{{/* Raw mail.log lines, long by nature: the whole column rather than the
+     reading measure (see the "wide" block in layout.html). */}}
+{{define "wide"}}wide{{end}}
+
+{{define "content"}}
+<h1>System log</h1>
+
+<div class="card">
+  <h2>Recent log entries</h2>
+  {{template "system_log_body" .}}
+</div>
+{{end}}