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/monitor.php

@@ -1,4 +1,50 @@
 <?php require_once dirname(__DIR__) . '/include/monitor.php'; ?>
+// ═══════════════════════════════════════════════════════════════════════════════════════════════
+// PURPOSE
+//   Monitor tab. The main dashboard — CPU per core, memory, GPUs, disks and pools, network,
+//   UPS, VMs, containers, transcodes, media sessions, and the watchdog health roll-up, for
+//   this host and every partner.
+//
+// DESIGN PRINCIPLES
+//   Two poll rates, deliberately split.
+//       api/monitor_fast.php carries the cheap, fast-moving values (1–2s); api/monitor.php
+//       carries the full payload on a slower cycle. Everything refreshing at the fast rate
+//       would put real load on the WebGUI this page exists to watch.
+//
+//   Served from the tmpfs cache, not live calls.
+//       api_cache_writer.sh refreshes the payload every minute and the endpoint serves that.
+//       ?live=1 bypasses it. A missing cache always falls back to a live call, so the cache
+//       can never be why the dashboard fails to load.
+//
+//   Missing subsystems simply do not render.
+//       No GPU, no UPS, no VMs — the corresponding card is absent rather than showing zeros
+//       or an error. The page is built to be correct on hardware lacking any given part.
+//
+// OPERATIONAL SAFEGUARDS
+//   The health roll-up must not default to healthy.
+//       vv_watchdog_summary() is conjunctive across every strike set, and it reads state from
+//       STATE_DIR. Six of those paths once pointed at /tmp, every read returned empty, and
+//       the page reported healthy unconditionally (fixed 2026-08-02). If this panel looks
+//       suspiciously green, verify the paths before believing it.
+//
+//   Container actions are confirmed and routed through the action endpoint, which validates
+//   against real inventory.
+//
+//   All remote and container-supplied strings render escaped.
+//
+// RENDERS
+//   System header, CPU per core, memory breakdown, GPU cards, storage pools and array disks,
+//   network, UPS, VMs, containers, transcode sessions, media now-playing, watchdog summary,
+//   partner node cards
+//
+// DEPENDS ON
+//   include/monitor.php     required directly for initial render
+//   api/monitor.php         full payload, slower cycle
+//   api/monitor_fast.php    fast-moving values, 1–2s
+//   api/system.php          system info
+//   api/media.php           now-playing sessions
+//   api/docker_action.php   container actions
+//   api/flag_toggle.php     toggles
 <style>
 @keyframes vvRsPulse {
   0%,100% { opacity:.5; transform:scaleX(.9); }