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/scheduler.php

@@ -1,4 +1,63 @@
 <?php
+// ═══════════════════════════════════════════════════════════════════════════════════════════════
+// PURPOSE
+//   Scheduler tab. The largest page in the plugin and the main operational surface: the full
+//   script library, per-job schedules, live run status and logs, dry-run output, conf editing
+//   per script, and the custom-script editor.
+//
+// OPERATIONAL MODEL
+//   Writes state that changes what the machine does on a timer. Enabling, disabling or
+//   rescheduling a job here takes effect on the next cron rebuild — this page decides what
+//   runs unattended at 1am.
+//
+// DESIGN PRINCIPLES
+//   Script descriptions come from the scripts themselves.
+//       Requires include/scheduler.php, which parses the PURPOSE block out of each bash
+//       header. The library listing and the script's own documentation are the same text and
+//       cannot drift. This page is the reason the repo-wide header convention exists.
+//
+//   The job tree is derived from conf, not maintained here.
+//       Orchestrator job lists come from master.conf arrays; custom scripts are whatever
+//       *.sh sits in CUSTOM_SCRIPTS_DIR. Nothing has to be registered in two places.
+//
+//   Long operations never block the page.
+//       Runs, dry-runs and imports go through api/run.php and api/dryrun.php with status
+//       polled separately, so a script that takes ten minutes does not hold a request open.
+//
+// OPERATIONAL SAFEGUARDS
+//   Running a script from the UI is confirmed first. Several of these delete files.
+//
+//   Dry-run is offered alongside run for anything destructive, and its output is shown in
+//   full rather than summarised — reading the list is the point.
+//
+//   Stale locks are cleared explicitly through api/clearlock.php, never automatically. A lock
+//   that looks stale may belong to a job still running.
+//
+//   Conf edits are surgical, preserving the comment blocks that document every threshold.
+//
+//   Custom scripts live outside the git repo, so a user's own scripts are never touched by a
+//   pull and never committed by accident.
+//
+//   Script content and log output render escaped throughout — this page displays arbitrary
+//   file contents.
+//
+// RENDERS
+//   Job tree by orchestrator tier, per-job schedule and toggle controls, live status and
+//   logs, dry-run output, per-script conf forms, custom script editor, run history
+//
+// DEPENDS ON
+//   include/scheduler.php  required directly — schedule, cron rebuild, script library
+//   api/scheduler.php      schedule read/write        api/run.php        execute
+//   api/dryrun.php         dry-run execute           api/stop.php       terminate
+//   api/status.php         live run status           api/log.php        log tail
+//   api/script.php         script read/write         api/readscript.php source
+//   api/scriptinfo.php     header metadata           api/import_script.php
+//   api/conf_toggle.php    per-script enable         api/flag_toggle.php
+//   api/confform.php       conf forms                api/rawconf.php    raw conf edit
+//   api/board.php          overview board            api/recent.php     recent runs
+//   api/snapshot.php       state snapshot            api/clearlock.php  stale lock clear
+//   api/savefolders.php    folder grouping           api/reorderarray.php
+//   api/rsync_standalone.php
 require_once dirname(__DIR__) . '/include/scheduler.php';
 
 // Setup mode — auto-open a conf file and force the editing sequence