feat(fc3c): SettingsView — Downloader section (rate limit + validate-files toggle)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/settings/ImportFiltersForm.vue

@@ -50,6 +50,28 @@
           <div class="fc-help">Higher = looser near-duplicate matching.</div>
         </v-col>
       </v-row>
+
+      <v-divider class="my-4" />
+      <div class="text-subtitle-2 mb-2">Downloader (FC-3c)</div>
+      <v-row>
+        <v-col cols="12" sm="6">
+          <v-text-field
+            v-model.number="local.download_rate_limit_seconds"
+            label="Rate limit (seconds between requests)"
+            type="number" step="0.5" min="0"
+            density="compact" hide-details @blur="save"
+          />
+          <div class="fc-help">gallery-dl extractor.sleep. Higher = slower but safer.</div>
+        </v-col>
+        <v-col cols="12" sm="6">
+          <v-switch
+            v-model="local.download_validate_files"
+            label="Validate downloaded files (magic-byte check)"
+            density="compact" hide-details color="accent" @change="save"
+          />
+        </v-col>
+      </v-row>
+
       <v-alert v-if="store.settingsError" type="error" variant="tonal" class="mt-2" closable>
         {{ store.settingsError }}
       </v-alert>
@@ -69,7 +91,9 @@ const local = reactive({
   min_width: 0, min_height: 0,
   skip_transparent: false, transparency_threshold: 0.9,
   skip_single_color: false, single_color_threshold: 0.95,
-  phash_threshold: 10
+  phash_threshold: 10,
+  download_rate_limit_seconds: 3.0,
+  download_validate_files: true,
 })
 
 watch(() => store.settings, (s) => { if (s) Object.assign(local, s) }, { immediate: true })