fix: enabled toggle — list-row click + edit-form save

Two bugs in the channel-enabled affordance:

1. List-row toggle was a static span with no handler; the row's
   row-link overlay swallowed every click and routed to /edit. Add
   POST /settings/notifications/{id}/toggle backed by a new store
   method SetNotificationChannelEnabled, and turn the row toggle
   into an htmx-driven button that swaps in the new state. Use
   event.stopPropagation() on the toggle so it beats the row link.

2. Edit-form toggle visually flipped but the underlying checkbox
   reverted: the visual span lives inside the <label>, so clicking
   it fired the inline JS handler AND the label's native
   checkbox-toggle, cancelling out. Bind to the checkbox 'change'
   event instead and let the label do the toggling — the JS just
   mirrors check.checked into the .on class.

web/templates/pages/settings.html

@@ -99,8 +99,18 @@
           <div class="mono text-ink-mute" style="overflow: hidden; text-overflow: ellipsis; white-space: nowrap;">
             {{if eq $ch.Kind "webhook"}}webhook · click to edit{{else if eq $ch.Kind "ntfy"}}ntfy · click to edit{{else}}smtp · click to edit{{end}}
           </div>
-          <div>
-            {{if $ch.Enabled}}<span class="toggle on"></span>{{else}}<span class="toggle"></span>{{end}}
+          <div class="row-action">
+            {{if $ch.Enabled}}
+              <span class="toggle on" hx-post="/settings/notifications/{{$ch.ID}}/toggle"
+                    hx-target="this" hx-swap="outerHTML"
+                    onclick="event.stopPropagation()" style="cursor:pointer"
+                    title="click to disable"></span>
+            {{else}}
+              <span class="toggle" hx-post="/settings/notifications/{{$ch.ID}}/toggle"
+                    hx-target="this" hx-swap="outerHTML"
+                    onclick="event.stopPropagation()" style="cursor:pointer"
+                    title="click to enable"></span>
+            {{end}}
           </div>
           <div class="mono text-ink-mid">
             {{if $ch.LastFiredAt}}{{relTime $ch.LastFiredAt}}{{else}}<span class="text-ink-fade">never</span>{{end}}
@@ -521,12 +531,16 @@ https://restic-manager.example/alerts/01KQTABCDEFGHJ</pre>
     });
   });
 
-  // Enabled toggle
+  // Enabled toggle: the visual <span class="toggle"> is inside a <label>
+  // wrapping a hidden checkbox, so clicking the span already flips the
+  // checkbox via the label's native behaviour. We only need to mirror
+  // that into the .on class — listening on the toggle's own click would
+  // race the label and cancel out, leaving check.checked at its original
+  // value (so Save would persist the unchanged setting).
   var check = document.getElementById('enabled-check');
   var tog   = document.getElementById('enabled-toggle');
   if (check && tog) {
-    tog.addEventListener('click', function() {
-      check.checked = !check.checked;
+    check.addEventListener('change', function() {
       tog.classList.toggle('on', check.checked);
     });
   }