feat: CS Monitor Issues — Explain button with step-by-step remediation

Each issue row now shows an Explain button (when a fix is available).
Clicking it expands an inline fix panel without navigating away from the
Issues tab. Clicking again (or the Close label) collapses it.

Fix content covers all current issue types:
  Security: admin username, db prefix, XML-RPC, readme/license exposure,
            PHP EOL, WP_DEBUG_DISPLAY, DISALLOW_FILE_EDIT/MODS,
            failed logins/brute force, author enumeration, plugin updates, HTTPS
  Performance: autoloaded options, WP-Cron backlog, slow queries, N+1 patterns,
               object cache hit rate, render-blocking scripts, asset bloat

Each fix panel includes: why it matters, numbered steps with inline code
snippets, and an advisory note where relevant. Click does not propagate to
the row's tab-switch handler.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Andrew Baker

assets/cs-perf-monitor.css

@@ -1273,6 +1273,78 @@ td.c-n { color: #555; font-size: 10px; text-align: right; padding-right: 6px; }
     text-overflow: ellipsis;
 }
 
+/* ── Explain / fix panel ─────────────────────────────────────────────────── */
+.cs-fix-btn {
+    flex-shrink: 0;
+    padding: 1px 7px;
+    font-size: 10px;
+    font-weight: 600;
+    background: #2a2d2e;
+    color: #9cdcfe;
+    border: 1px solid #3a3d3e;
+    border-radius: 3px;
+    cursor: pointer;
+    letter-spacing: .02em;
+    line-height: 16px;
+    transition: background .1s, color .1s;
+}
+.cs-fix-btn:hover     { background: #3a3d3e; color: #fff; }
+.cs-fix-btn-active    { background: #1e3a4a; color: #4ec9b0; border-color: #4ec9b0; }
+
+.cs-fix-wrap {
+    display: none;
+    margin: 6px 0 2px;
+}
+.cs-fix-wrap.cs-fix-open { display: block; }
+
+.cs-fix-panel {
+    background: #161616;
+    border: 1px solid #2a2a2a;
+    border-radius: 4px;
+    padding: 10px 12px;
+    font-size: 11px;
+}
+.cs-fix-why {
+    color: #9e9e9e;
+    font-style: italic;
+    margin-bottom: 8px;
+    line-height: 1.5;
+    border-left: 2px solid #3a3d3e;
+    padding-left: 8px;
+}
+.cs-fix-steps {
+    margin: 0;
+    padding-left: 20px;
+    counter-reset: fix-step;
+}
+.cs-fix-steps li {
+    color: #d4d4d4;
+    line-height: 1.55;
+    margin-bottom: 5px;
+    list-style-type: decimal;
+}
+.cs-fix-steps li:last-child { margin-bottom: 0; }
+.cs-fix-steps code {
+    font-family: 'Consolas', 'Monaco', monospace;
+    font-size: 10.5px;
+    background: #252526;
+    color: #ce9178;
+    padding: 1px 4px;
+    border-radius: 2px;
+    white-space: nowrap;
+}
+.cs-fix-steps b { color: #e6c949; font-weight: 600; }
+.cs-fix-note {
+    margin-top: 8px;
+    padding: 5px 8px;
+    background: #1e2a1e;
+    border-left: 2px solid #4ec9b0;
+    color: #888;
+    font-size: 10px;
+    line-height: 1.5;
+    border-radius: 0 3px 3px 0;
+}
+
 /* ── Request tab ─────────────────────────────────────────────────────────── */
 .cs-request-wrap { padding: 0; }
 .cs-req-body { padding: 8px 10px 16px; }