Phase 1 MVP: drop-in step registry + session + Markdown report

Plugin skeleton, drop-in step registry, option-backed session, single-page
checklist UI, downloadable Markdown report. Steps live as one file each
under includes/steps/ — adding/removing one is a single file change.
Step IDs are stable strings so renaming files preserves session data.

Architecture (hc-5ix.3): WPH_Steps singleton globs includes/steps/*.php,
natsort-orders by filename, requires each file (which returns a WPH_Step
instance), then applies a 'wph_steps' filter so installs can drop steps.

Session (hc-5ix.4): option-backed (per decision — plugin is installed
per-engagement, so DB-resident history would be lost on uninstall).
Single in-progress session per site; finished sessions render a report
that the user downloads/copies.

Recovery bootstrap (hc-5ix.1): detects whether wp-site-recovery is
installed + active, surfaces state on the start panel and in every
active session. Manual install for now; private update channel deferred
to hc-5ix.27.

Smoke-tested on testsite: registry discovery (13 steps in correct order),
start → update_step → progress count → finish → 8KB Markdown report →
discard cycle.

includes/steps/20-environment.php

@@ -0,0 +1,19 @@
+<?php
+if (!defined('ABSPATH')) exit;
+
+return new class extends WPH_Step {
+    public function id(): string { return 'environment'; }
+    public function title(): string { return 'Step 2 — Environment Check'; }
+    public function blurb(): string {
+        return 'Before touching updates, review the hosting environment.';
+    }
+    public function sub_items(): array {
+        return [
+            'PHP version — check against WordPress requirements and plugin compatibility. Flag if below 8.1. Note if EOL.',
+            'Disk usage — flag if over 80% used',
+            'Error logs — check the server error log and WordPress debug log if enabled. Note any recurring errors, 500s, or deprecated function warnings',
+            'wp-config.php — confirm WP_DEBUG is off on production',
+            'File permissions — spot check wp-config.php (should be 640 or 600), wp-content (755), uploads (755)',
+        ];
+    }
+};