Add metrics password override and implement frontend UI indicators

Backend changes:
- Added WG_METRICS_PASSWORD environment variable override
- Updated applyGeneralOverrides() to include metrics password
- Updated /api/admin/overrides endpoint to include metrics password

Frontend changes:
- Added override indicators (warning icons with tooltips) to all form fields
- Updated TextField, NumberField, NullTextField, SwitchField, HostField, ArrayField components
- Added overridden prop support to all form components
- Fetched /api/admin/overrides in all admin pages (interface, general, config, hooks)
- Warning icon displays when field is overridden by environment variable
- ArrayField shows banner when overridden
- Updated documentation with WG_METRICS_PASSWORD

Co-authored-by: kaaax0815 <32197462+kaaax0815@users.noreply.github.com>

src/app/components/Form/HostField.vue

@@ -6,6 +6,9 @@
     <BaseTooltip v-if="description" :text="description">
       <IconsInfo class="size-4" />
     </BaseTooltip>
+    <BaseTooltip v-if="overridden" text="This field is overridden by an environment variable">
+      <IconsWarning class="size-4 ml-1 text-amber-500" />
+    </BaseTooltip>
   </div>
   <div class="flex gap-1">
     <BaseInput
@@ -38,6 +41,7 @@ defineProps<{
   description?: string;
   placeholder?: string;
   url: '/api/admin/ip-info' | '/api/setup/4';
+  overridden?: boolean;
 }>();
 
 const data = defineModel<string | null>({