fix(js): resolve ESLint no-undef warnings across 6 JS files

Three distinct patterns:

1. Vendor library globals — htmx is injected by <script> before these
   extension files load; ESLint lints files in isolation and doesn't know.
   Fix: add /* global htmx */ to htmx-sse.js and htmx-json-enc.js.

2. Cross-file globals — showNotification is defined as window.showNotification
   in app.js/notification.js but called bare in app.js and error_handler.js.
   ESLint doesn't connect window.X = Y with a bare call to X.
   Fix: add /* global showNotification */ to app.js and error_handler.js.

3. Forward-reference window.* functions — in array-table.js, checkbox-group.js,
   and custom-feeds.js, functions like removeArrayTableRow are called early
   inside event-handler closures but assigned to window.* later in the file.
   At runtime this works (the handler fires after the assignment), but ESLint
   sees the bare name at the call site.
   Fix: change bare calls to window.removeArrayTableRow(this) etc. so the
   reference is explicit and ESLint-safe.

Also guard the updateSystemStats call in app.js reconnectSSE: the function
is called but defined nowhere in the codebase. Guard with typeof check so
it won't throw ReferenceError if the reconnect path is hit.

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

web_interface/static/v3/app.js

@@ -1,3 +1,4 @@
+/* global showNotification */
 // LED Matrix v3 JavaScript
 // Additional helpers for HTMX and Alpine.js integration
 
@@ -57,7 +58,7 @@ window.reconnectSSE = function() {
         window.statsSource = new EventSource('/api/v3/stream/stats');
         window.statsSource.onmessage = function(event) {
             const data = JSON.parse(event.data);
-            updateSystemStats(data);
+            if (typeof updateSystemStats === 'function') updateSystemStats(data);
         };
     }
 

web_interface/static/v3/js/htmx-json-enc.js

@@ -1,3 +1,4 @@
+/* global htmx */
 htmx.defineExtension('json-enc', {
     onEvent: function (name, evt) {
         if (name === "htmx:configRequest") {

web_interface/static/v3/js/htmx-sse.js

@@ -1,3 +1,4 @@
+/* global htmx */
 /*
 Server Sent Events Extension
 ============================

web_interface/static/v3/js/utils/error_handler.js

@@ -1,3 +1,4 @@
+/* global showNotification */
 /**
  * Frontend error handling utilities.
  *

web_interface/static/v3/js/widgets/array-table.js

@@ -179,7 +179,7 @@
         const removeButton = document.createElement('button');
         removeButton.type = 'button';
         removeButton.className = 'text-red-600 hover:text-red-800 px-2 py-1';
-        removeButton.onclick = function() { removeArrayTableRow(this); };
+        removeButton.onclick = function() { window.removeArrayTableRow(this); };
         const removeIcon = document.createElement('i');
         removeIcon.className = 'fas fa-trash';
         removeButton.appendChild(removeIcon);

web_interface/static/v3/js/widgets/checkbox-group.js

@@ -75,7 +75,7 @@
             });
             
             // Update hidden input
-            updateCheckboxGroupData(fieldId);
+            window.updateCheckboxGroupData(fieldId);
         },
         
         handlers: {

web_interface/static/v3/js/widgets/custom-feeds.js

@@ -142,7 +142,7 @@
                 fileInput.dataset.index = String(index);
                 fileInput.addEventListener('change', function(e) {
                     const idx = parseInt(e.target.dataset.index || '0', 10);
-                    handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
+                    window.handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
                 });
                 
                 const uploadButton = document.createElement('button');
@@ -207,7 +207,7 @@
                 removeButton.type = 'button';
                 removeButton.className = 'text-red-600 hover:text-red-800 px-2 py-1';
                 removeButton.addEventListener('click', function() {
-                    removeCustomFeedRow(this);
+                    window.removeCustomFeedRow(this);
                 });
                 const removeIcon = document.createElement('i');
                 removeIcon.className = 'fas fa-trash';
@@ -290,7 +290,7 @@
         fileInput.dataset.index = String(newIndex);
         fileInput.addEventListener('change', function(e) {
             const idx = parseInt(e.target.dataset.index || '0', 10);
-            handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
+            window.handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
         });
         
         const uploadButton = document.createElement('button');
@@ -449,7 +449,7 @@
                     fileInput.dataset.index = String(index);
                     fileInput.addEventListener('change', function(e) {
                         const idx = parseInt(e.target.dataset.index || '0', 10);
-                        handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
+                        window.handleCustomFeedLogoUpload(e, fieldId, idx, pluginId, fullKey);
                     });
                     
                     // Create upload button