Add Varaverk plugin scaffold (PHP, unRAID native)

Plugin lives in Plugin/ — invisible to User Script Plugin.
dev_install.sh symlinks into /usr/local/emhttp/plugins/varaverk/ for development.

Pages: Monitor (5s poll), Scheduler (orchs + Advanced children, toggle + cron),
Config (raw editor, host-aware file access), Docs (markdown + live $VAR substitution).

API endpoints: monitor.php (JSON), scheduler.php (writes schedule.json + cron.d),
config.php (writes conf files with host permission check).

Includes: config.php (parser, host detection, var map), scheduler.php (job tree,
cron.d rebuild), monitor.php (docker, GPU, resources, fallback, transcode),
docs.php (file tree, var substitution, Parsedown renderer).

Plugin/usr/local/emhttp/plugins/varaverk/api/monitor.php

@@ -0,0 +1,14 @@
+<?php
+header('Content-Type: application/json');
+require_once dirname(__DIR__) . '/include/monitor.php';
+
+echo json_encode([
+    'fallback'    => vv_fallback_state(),
+    'resources'   => vv_system_resources(),
+    'gpu'         => vv_gpu_stats(),
+    'gpu_procs'   => vv_gpu_processes(),
+    'containers'  => vv_docker_containers(),
+    'stopped'     => vv_docker_stopped(),
+    'transcode'   => vv_transcode_sessions(),
+    'ts'          => time(),
+]);