Add structured headers to the PHP pages layer

Documents each tab's purpose, what it renders, and which endpoints it polls.
Pages that start with markup get the header in a <?php ?> block so it never
reaches the browser.

Also corrects the layer diagram in README-unraid.md: eight of eleven pages hold
no PHP logic and poll api/ for everything — only auth, monitor and scheduler
require an include/ file directly.

Plugin/unraid/pages/arrs.php

@@ -1,3 +1,31 @@
+<?php
+// ═══════════════════════════════════════════════════════════════════════════════════════════════
+// PURPOSE
+//   Arrs tab. Library counts, queue state, root folders and recent cleanup/discovery activity
+//   for every Sonarr / Radarr / Lidarr instance across all nodes.
+//
+// DESIGN PRINCIPLES
+//   Pure view — markup plus a poll against api/arrs.php. Instance discovery, live fetching
+//   and stats parsing all live in include/arrs.php.
+//
+//   Local nodes are live, remote nodes are cached. The page surfaces cache age rather than
+//   hiding it, so a 2-hour-old partner count is never presented as current.
+//
+// OPERATIONAL SAFEGUARDS
+//   Read-only with respect to media. Nothing here triggers a scan, import, or deletion —
+//   the arr cleanups are scheduled scripts, not page buttons.
+//
+//   A node with no cache yet renders as "not collected", distinct from a node that genuinely
+//   has an empty library.
+//
+// RENDERS
+//   Per-node arr cards: tracked counts, queue, root folders, cleanup and discovery stats
+//   Inline conf editing for arr-related settings
+//
+// DEPENDS ON
+//   api/arrs.php      polled every 60s   → include/arrs.php
+//   api/confform.php  inline conf edits  → include/confform.php
+?>
 <style>
 /* ── Cards ───────────────────────────────────────────────── */
 .vv-arr-card  { background:#161616;border:1px solid #2a2a2a;border-radius:6px;padding:12px 14px;min-width:0; }