feat(settings-ui): expose dashboard failure threshold

frontend/src/views/Settings.vue

@@ -62,6 +62,24 @@
 
           <v-divider class="my-6" />
 
+          <!-- Dashboard Settings -->
+          <h3 class="text-h6 mb-4">Dashboard</h3>
+          <v-row>
+            <v-col cols="12" md="6">
+              <v-text-field
+                v-model.number="settings['dashboard.failure_threshold']"
+                label="Failing source threshold"
+                type="number"
+                min="1"
+                max="20"
+                hint="Consecutive download failures before a source is marked failing. One success resets the counter."
+                persistent-hint
+              />
+            </v-col>
+          </v-row>
+
+          <v-divider class="my-6" />
+
           <!-- Notification Settings -->
           <h3 class="text-h6 mb-4">Notifications</h3>
           <v-row>