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/SwitchField.vue

@@ -6,11 +6,19 @@
     <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>
   <BaseSwitch :id="id" v-model="data" />
 </template>
 
 <script lang="ts" setup>
-defineProps<{ id: string; label: string; description?: string }>();
+defineProps<{
+  id: string;
+  label: string;
+  description?: string;
+  overridden?: boolean;
+}>();
 const data = defineModel<boolean>();
 </script>