Theme step: identify removal candidates explicitly

Replaces the 'inactive themes count' finding with a clearer breakdown:

Keep set (each gets a 'Keep — <why>' row):
- The active theme (always)
- The parent of the active theme (if a child theme is in use and
  the parent exists on disk)
- The newest Twenty* default installed (as a fallback we can swap
  to if the active theme breaks during work)

Removal candidates (one row per inactive theme not in the keep set):
- 'Candidate' rows for the technician to walk down and remove
- Summary line warns at >3 candidates
- 'none' ok row if every installed theme is a keeper

Smoke-tested on testsite with three configurations:
- Default theme active, no child: keep active + Twenty Twenty-Five
  fallback; one removal candidate.
- Cluttered (Astra + Hello Elementor + extra Twenty* installed):
  same keepers, 4 candidates surfaced.
- Astra active (custom, no child): keep Astra + Twenty Twenty-Five
  fallback; 4 candidates including any unused Twenty* and Hello
  Elementor.

includes/steps/50-theme.php

@@ -78,20 +78,82 @@ return new class extends WPH_Step {
             $f[] = $this->finding('active_update', 'ok', 'Active theme update', 'up to date', '');
         }
 
-        // Inactive themes
+        // --- Themes to keep vs. removal candidates ---------------------------
+        // Keep: the active theme, its parent (if a child), and the newest default
+        // Twenty* theme installed (as a fallback we can swap to if the active
+        // theme breaks during work). Everything else is a removal candidate.
         $all = wp_get_themes();
-        $inactive = [];
-        foreach ($all as $slug => $t) {
-            if ($slug === $active->get_stylesheet() || ($is_child && $slug === $parent->get_stylesheet())) continue;
-            $inactive[$slug] = (string) $t->get('Name');
+
+        $keep_slugs = [$active->get_stylesheet()];
+        $keep_reasons = [$active->get_stylesheet() => 'active theme'];
+        if ($is_child && $parent && $parent->exists()) {
+            $parent_slug = $parent->get_stylesheet();
+            $keep_slugs[] = $parent_slug;
+            $keep_reasons[$parent_slug] = 'parent of active theme';
         }
+
+        // Find the newest default theme installed (priority by release year).
+        $default_priority = [
+            'twentytwentyfive', 'twentytwentyfour', 'twentytwentythree',
+            'twentytwentytwo',  'twentytwentyone',  'twentytwenty',
+            'twentynineteen',   'twentyseventeen',  'twentysixteen',
+            'twentyfifteen',    'twentyfourteen',   'twentythirteen',
+            'twentytwelve',     'twentyeleven',     'twentyten',
+        ];
+        $fallback_slug = null;
+        foreach ($default_priority as $slug) {
+            if (isset($all[$slug])) {
+                $fallback_slug = $slug;
+                break;
+            }
+        }
+        if ($fallback_slug && !in_array($fallback_slug, $keep_slugs, true)) {
+            $keep_slugs[] = $fallback_slug;
+            $keep_reasons[$fallback_slug] = 'fallback default (newest Twenty* installed)';
+        } elseif ($fallback_slug && in_array($fallback_slug, $keep_slugs, true)) {
+            // Active theme already is the newest Twenty* — note it but no extra entry.
+            $keep_reasons[$fallback_slug] .= ' (also serves as the default fallback)';
+        }
+
+        // Emit keeper rows (ok level).
+        foreach ($keep_slugs as $slug) {
+            if (!isset($all[$slug])) continue; // theme missing on disk
             $f[] = $this->finding(
-            'inactive_themes',
-            count($inactive) > 3 ? 'warn' : 'info',
-            'Inactive themes',
-            (string) count($inactive),
-            $inactive ? implode(', ', array_slice($inactive, 0, 6)) . (count($inactive) > 6 ? ' …' : '') : ''
+                'keep_' . sanitize_key($slug),
+                'ok',
+                'Keep — ' . $keep_reasons[$slug],
+                (string) $all[$slug]->get('Name') . ' (' . $slug . ')',
+                ''
             );
+        }
+
+        // Emit removal candidates (info level).
+        $candidates = [];
+        foreach ($all as $slug => $t) {
+            if (in_array($slug, $keep_slugs, true)) continue;
+            $candidates[$slug] = (string) $t->get('Name');
+        }
+        if (!$candidates) {
+            $f[] = $this->finding('rm_none', 'ok', 'Removal candidates', 'none', 'No inactive themes left to clear out.');
+        } else {
+            // Summary line first, then each candidate.
+            $f[] = $this->finding(
+                'rm_count',
+                count($candidates) > 3 ? 'warn' : 'info',
+                'Removal candidates',
+                count($candidates) . ' theme(s)',
+                'Inactive themes that aren\'t the active theme, its parent, or the fallback default — safe to remove unless flagged by the client.'
+            );
+            foreach ($candidates as $slug => $name) {
+                $f[] = $this->finding(
+                    'rm_' . sanitize_key($slug),
+                    'info',
+                    'Candidate',
+                    $name . ' (' . $slug . ')',
+                    'Delete via Appearance → Themes if not needed.'
+                );
+            }
+        }
 
         return $f;
     }