refactor: migrate DataExportSection to PlatformServiceMixin

- Use PlatformServiceMixin for platform and database access
- Replace manual PlatformService instantiation with mixin methods/properties
- Use $contacts() for contact export
- Use capabilities for platform checks in template and logic
- Remove unused imports and redundant code
- Lint clean

src/components/UsageLimitsSection.vue

@@ -2,7 +2,9 @@
   <section class="mt-4">
     <h2 class="text-lg font-semibold mb-2">Usage Limits</h2>
     <div class="mb-2">
-      <span v-if="loadingLimits" class="text-slate-700">Checking... <span class="animate-spin">⏳</span></span>
+      <span v-if="loadingLimits" class="text-slate-700"
+        >Checking... <span class="animate-spin">⏳</span></span
+      >
       <span v-else class="text-slate-700">{{ limitsMessage }}</span>
     </div>
     <button
@@ -15,14 +17,14 @@
 </template>
 
 <script lang="ts">
-import { Component, Vue, Prop, Emit } from 'vue-facing-decorator';
+import { Component, Vue, Prop, Emit } from "vue-facing-decorator";
 
-@Component({ name: 'UsageLimitsSection' })
+@Component({ name: "UsageLimitsSection" })
 export default class UsageLimitsSection extends Vue {
   @Prop({ required: true }) loadingLimits!: boolean;
   @Prop({ required: true }) limitsMessage!: string;
 
-  @Emit('recheck-limits')
+  @Emit("recheck-limits")
   recheckLimits() {}
 }
-</script> 
+</script>