Fix checkbox/label spacing on Notifications and other form checkboxes

Tabler's form-check-single modifier zeroes margin on .form-check-input,
which cancels the -2rem margin-inline-start the base .form-check rule
relies on to offset the checkbox into its label's padding gutter. That
left checkboxes floating almost flush against their label text.

Removed the form-check-single class from all 9 affected checkboxes:
6 in NotificationSettings, 1 each in DnsProviderForm, IntegrationForm,
and IntegrationEditForm.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/components/DnsProviderForm.tsx

@@ -108,7 +108,7 @@ export default function DnsProviderForm({
           {fields.map((field) => (
             <div className="col-md-4" key={field.key}>
               {field.type === "checkbox" ? (
-                <label className="form-check form-check-single mt-4">
+                <label className="form-check mt-4">
                   <input
                     type="checkbox"
                     className="form-check-input"

web/src/components/IntegrationEditForm.tsx

@@ -116,7 +116,7 @@ export default function IntegrationEditForm({
           {fields?.map((field) => (
             <div className="col-md-4" key={field.key}>
               {field.type === "checkbox" ? (
-                <label className="form-check form-check-single mt-4">
+                <label className="form-check mt-4">
                   <input
                     type="checkbox"
                     className="form-check-input"

web/src/components/IntegrationForm.tsx

@@ -119,7 +119,7 @@ export default function IntegrationForm({ onCreated, onCancel }: { onCreated: ()
           {fields.map((field) => (
             <div className="col-md-4" key={field.key}>
               {field.type === "checkbox" ? (
-                <label className="form-check form-check-single mt-4">
+                <label className="form-check mt-4">
                   <input
                     type="checkbox"
                     className="form-check-input"

web/src/pages/settings/NotificationSettings.tsx

@@ -185,7 +185,7 @@ export default function NotificationSettings() {
             </div>
             <div className="card-body">
               <p className="text-secondary">Send push notifications to a self-hosted Gotify instance.</p>
-              <label className="form-check form-check-single mb-3">
+              <label className="form-check mb-3">
                 <input
                   type="checkbox"
                   className="form-check-input"
@@ -250,7 +250,7 @@ export default function NotificationSettings() {
               <p className="text-secondary">
                 Send notifications via <a href="https://ntfy.sh" target="_blank" rel="noreferrer">ntfy.sh</a> or a self-hosted instance.
               </p>
-              <label className="form-check form-check-single mb-3">
+              <label className="form-check mb-3">
                 <input
                   type="checkbox"
                   className="form-check-input"
@@ -324,7 +324,7 @@ export default function NotificationSettings() {
             </div>
             <div className="card-body">
               <p className="text-secondary">Send notifications via email using any SMTP server.</p>
-              <label className="form-check form-check-single mb-3">
+              <label className="form-check mb-3">
                 <input
                   type="checkbox"
                   className="form-check-input"
@@ -356,7 +356,7 @@ export default function NotificationSettings() {
                   />
                 </div>
               </div>
-              <label className="form-check form-check-single mb-3">
+              <label className="form-check mb-3">
                 <input
                   type="checkbox"
                   className="form-check-input"
@@ -434,7 +434,7 @@ export default function NotificationSettings() {
               <p className="text-secondary">
                 POST a JSON payload to any HTTP endpoint. Uses Discord/Slack-compatible <code>{"{ \"content\": \"…\" }"}</code> format.
               </p>
-              <label className="form-check form-check-single mb-3">
+              <label className="form-check mb-3">
                 <input
                   type="checkbox"
                   className="form-check-input"
@@ -490,7 +490,7 @@ export default function NotificationSettings() {
                 { key: "secretCheck" as const, label: "Secret expiry reminder" },
                 { key: "tailscaleKeyCheck" as const, label: "Tailscale key expiry reminder" },
               ].map(({ key, label }) => (
-                <label key={key} className="form-check form-check-single mb-2">
+                <label key={key} className="form-check mb-2">
                   <input
                     type="checkbox"
                     className="form-check-input"