Reorganize PHP internals and static assets

Move shared PHP code into private/, move JavaScript files into js/, and block direct access to private/. Remove unused API key and cache artifacts from the working tree.

js/clipboard.js

@@ -0,0 +1,56 @@
+(function () {
+    'use strict';
+
+    function fallbackCopy(text) {
+        const input = document.createElement('textarea');
+        input.value = text;
+        input.setAttribute('readonly', 'readonly');
+        input.style.position = 'fixed';
+        input.style.left = '-9999px';
+        document.body.appendChild(input);
+        input.select();
+
+        try {
+            document.execCommand('copy');
+        } finally {
+            document.body.removeChild(input);
+        }
+    }
+
+    function copyText(text) {
+        if (navigator.clipboard && navigator.clipboard.writeText) {
+            return navigator.clipboard.writeText(text);
+        }
+
+        fallbackCopy(text);
+        return Promise.resolve();
+    }
+
+    function showCopied(button) {
+        const original = button.dataset.copyLabel || button.textContent;
+        const copied = button.dataset.copiedLabel || 'Copied';
+
+        button.textContent = copied;
+        window.setTimeout(function () {
+            button.textContent = original;
+        }, 1400);
+    }
+
+    document.addEventListener('DOMContentLoaded', function () {
+        document.querySelectorAll('.js-copy-button').forEach(function (button) {
+            button.addEventListener('click', function () {
+                let text = button.dataset.copyText || '';
+                const targetId = button.dataset.copyTarget || '';
+                const target = targetId ? document.getElementById(targetId) : null;
+
+                if (target) {
+                    text = target.value || target.textContent || '';
+                }
+
+                copyText(text).then(function () {
+                    showCopied(button);
+                });
+            });
+        });
+    });
+}());