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/fallback.php

@@ -1,3 +1,35 @@
+<?php
+// ═══════════════════════════════════════════════════════════════════════════════════════════════
+// PURPOSE
+//   Fallback tab. Current state of every node (NORMAL / FALLBACK / NO_INTERNET / DARK),
+//   which tiers have activated, handback strike progress, and which covered containers are
+//   actually running.
+//
+// DESIGN PRINCIPLES
+//   Pure view — markup plus a poll against api/fallback.php. State parsing lives in
+//   include/fallback.php.
+//
+//   Reports what each node believes about itself. Remote state is read from the partner's own
+//   state file rather than inferred from what this host can reach.
+//
+//   Polls faster than most tabs (30s) because this is the page someone opens during an
+//   outage, when stale numbers are actively misleading.
+//
+// OPERATIONAL SAFEGUARDS
+//   Read-only. The page cannot trigger a failover, force a handback, or start a covered
+//   container. Fallback is driven by fallback.sh reacting to real reachability, and a manual
+//   override from a browser is exactly the wrong way to enter that state.
+//
+//   A missing state file renders as unknown, never as NORMAL — claiming healthy for a
+//   fallback process that is not running would be the worst possible error on this page.
+//
+// RENDERS
+//   Per-node state, tier activation and delays, handback strikes, covered container status
+//
+// DEPENDS ON
+//   api/fallback.php  polled every 30s   → include/fallback.php
+//   api/confform.php  inline conf edits  → include/confform.php
+?>
 <style>
 /* ── Existing status styles ── */
 .vv-fb-active   { background:#1a1200;border:1px solid #5a3800;border-radius:6px;padding:12px 14px; }