fix: array-table boolean columns always saved as unchecked (#381)

Reported bug: countdown plugin always shows "No Active" even with a
countdown configured and enabled — because every save silently unchecked
it. Root cause: the boolean column's hidden-sentinel input (needed so
unchecked checkboxes still submit "false", since browsers omit unchecked
checkboxes entirely) was hardcoded to value="false" and shared the same
`name` as the checkbox, with no sync between them. Whichever of the two
same-named inputs the save request's form-collection happens to prefer,
the hidden's stale "false" could silently override an actually-checked
box on every save, independent of what the user set.

Fixed in both places this pattern is rendered:
- plugin_config.html: the initial server-rendered row for every array-table
  boolean column (affects countdown's per-countdown "enabled" and the
  custom-feeds widget's per-feed "enabled") — now sets the hidden's initial
  value from the actual data, and syncs it via onchange on every toggle.
- array-table.js: the client-side row renderer used when adding/rebuilding
  rows in the browser — same fix, keeping both inputs in sync at render
  time and via a change listener.

Verified other checkbox/hidden-input patterns in plugin_config.html and
confirmed they're unrelated/already-safe: the default single-checkbox
renderer (no hidden pair), checkbox-group (array-bracket names with its
own explicit sync), the array-table advanced-props modal editor (single
hidden per name, explicitly written on Save), the top-level plugin
enable/disable toggle (separate immediate hx-post), and the no-schema
fallback checkbox. custom-feeds.js's own client-side row renderer never
creates a hidden sentinel at all, so it isn't affected either.

Verified the fix's rendered output directly with an isolated Jinja render
of the exact snippet: hidden and checkbox now agree ("true"/checked or
"false"/unchecked) for both states, where before the hidden was always
"false" regardless of the actual value.


Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

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

@@ -174,11 +174,16 @@
         cell.style.verticalAlign = 'middle';
 
         if (colType === 'boolean') {
-            // Boolean: hidden sentinel + visible checkbox
+            // Boolean: hidden sentinel + visible checkbox, same `name` (so
+            // unchecked boxes still submit "false"). Keep the hidden's value
+            // synced to the checkbox at all times — some form-collection
+            // paths prefer whichever of the two same-named inputs comes
+            // first/last in the DOM, and a stale hidden value previously
+            // caused this field to silently revert to false on every save.
             const hidden = document.createElement('input');
             hidden.type  = 'hidden';
             hidden.name  = inputName;
-            hidden.value = 'false';
+            hidden.value = String(Boolean(colValue));
             cell.appendChild(hidden);
 
             const cb = document.createElement('input');
@@ -187,6 +192,9 @@
             cb.checked   = Boolean(colValue);
             cb.value     = 'true';
             cb.className = 'h-4 w-4 text-blue-600';
+            cb.addEventListener('change', () => {
+                hidden.value = String(cb.checked);
+            });
             cell.appendChild(cb);
 
         } else if (colType === 'integer' || colType === 'number') {