fix: add null checks and error handling to docs JS controllers

clipboard_controller.js:
- Check if clipboard API is available before using
- Handle clipboard write promise rejection
- Show error icon on failure

prev-next_controller.js:
- Guard against missing navigation element
- Guard against missing span element in links

anchor_controller.js:
- Guard against missing ul element

docs/assets/js/controllers/anchor_controller.js

@@ -15,6 +15,12 @@ export default class extends Controller {
 
     createAnchorNavigation() {
         const ul = this.container.querySelector('ul')
+
+        // Guard against missing ul element
+        if (!ul) {
+            return
+        }
+
         const anchors = document.querySelectorAll('#main-article h3, #main-article h2, #main-article a.anchor')
 
         if (anchors.length === 0) {

docs/assets/js/controllers/clipboard_controller.js

@@ -20,7 +20,7 @@ export default class extends Controller {
 
             parent.append(button)
 
-            button.addEventListener('click', () => {
+            button.addEventListener('click', async () => {
                 let code = codeBlock.textContent.trim()
                 if (code.startsWith('#')) {
                     const parts = code.split('\n')
@@ -28,9 +28,19 @@ export default class extends Controller {
                     code = parts.join('\n')
                 }
 
-                window.navigator.clipboard.writeText(code)
+                // Check if clipboard API is available
+                if (!window.navigator?.clipboard?.writeText) {
+                    console.warn('Clipboard API not available')
+                    return
+                }
 
-                button.innerHTML = '<i class="fa-duotone fa-clipboard-check"></i>'
+                try {
+                    await window.navigator.clipboard.writeText(code)
+                    button.innerHTML = '<i class="fa-duotone fa-clipboard-check"></i>'
+                } catch (error) {
+                    console.error('Failed to copy to clipboard:', error)
+                    button.innerHTML = '<i class="fa-duotone fa-clipboard-question"></i>'
+                }
 
                 setTimeout(() => {
                     button.innerHTML = icon

docs/assets/js/controllers/prev-next_controller.js

@@ -4,6 +4,12 @@ export default class extends Controller {
     connect() {
         const prevNext = document.querySelectorAll('.prev-next')
         const navigation = document.getElementById('main-navigation')
+
+        // Guard against missing navigation element
+        if (!navigation) {
+            return
+        }
+
         const navigationLinks = navigation.querySelectorAll('a')
 
         let previous
@@ -15,6 +21,10 @@ export default class extends Controller {
 
             links.forEach((link) => {
                 const label = link.querySelector('span')
+                // Guard against missing span element
+                if (!label) {
+                    return
+                }
                 label.innerHTML = originalLink.innerHTML.replace(/\d+\. /, '').replace(/<(\S*?)[^>]*>.*?<\/\1>|<.*?\/>/, '')
                 link.href = originalLink.href
                 link.classList.remove('hidden')