feat: external Learning Hub toggle + applicant help button

- Add admin settings: learning_hub_external, learning_hub_external_url, support_email
- Jury/Mentor nav respects external Learning Hub URL (opens in new tab)
- RoleNav supports external nav items with ExternalLink icon
- Applicant header shows Help button with configurable support email
- Settings update mutation now upserts (creates on first use)
- Shared inferSettingCategory for consistent category assignment

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

src/components/settings/settings-content.tsx

@@ -123,6 +123,9 @@ export function SettingsContent({ initialSettings, isSuperAdmin = true }: Settin
     'default_page_size',
     'autosave_interval_seconds',
     'display_project_names_uppercase',
+    'learning_hub_external',
+    'learning_hub_external_url',
+    'support_email',
   ])
 
   const digestSettings = getSettingsByKeys([
@@ -432,7 +435,7 @@ export function SettingsContent({ initialSettings, isSuperAdmin = true }: Settin
         </TabsContent>
       )}
 
-      <TabsContent value="defaults">
+      <TabsContent value="defaults" className="space-y-6">
         <AnimatedCard>
         <Card>
           <CardHeader>
@@ -446,6 +449,20 @@ export function SettingsContent({ initialSettings, isSuperAdmin = true }: Settin
           </CardContent>
         </Card>
         </AnimatedCard>
+
+        <AnimatedCard>
+        <Card>
+          <CardHeader>
+            <CardTitle>Platform Features</CardTitle>
+            <CardDescription>
+              Configure Learning Hub, support contact, and other platform features
+            </CardDescription>
+          </CardHeader>
+          <CardContent>
+            <PlatformFeaturesSection settings={defaultsSettings} />
+          </CardContent>
+        </Card>
+        </AnimatedCard>
       </TabsContent>
 
       <TabsContent value="digest" className="space-y-6">
@@ -805,6 +822,37 @@ function AuditSettingsSection({ settings }: { settings: Record<string, string> }
   )
 }
 
+function PlatformFeaturesSection({ settings }: { settings: Record<string, string> }) {
+  return (
+    <div className="space-y-6">
+      <div className="space-y-4">
+        <Label className="text-sm font-medium">Learning Hub</Label>
+        <SettingToggle
+          label="Use External Learning Hub"
+          description="When enabled, jury and mentor navigation links will open the external URL instead of the built-in Learning Hub"
+          settingKey="learning_hub_external"
+          value={settings.learning_hub_external || 'false'}
+        />
+        <SettingInput
+          label="External URL"
+          description="The URL to redirect jury and mentor users to (e.g. Google Drive, Notion, etc.)"
+          settingKey="learning_hub_external_url"
+          value={settings.learning_hub_external_url || ''}
+        />
+      </div>
+      <div className="border-t pt-4 space-y-4">
+        <Label className="text-sm font-medium">Support</Label>
+        <SettingInput
+          label="Support Email"
+          description="Shown as a help button on the applicant page header. Leave empty to hide."
+          settingKey="support_email"
+          value={settings.support_email || ''}
+        />
+      </div>
+    </div>
+  )
+}
+
 function WhatsAppSettingsSection({ settings }: { settings: Record<string, string> }) {
   return (
     <div className="space-y-4">