feat(05-07): 3-tab SettingsView, SettingsCloudTab, CloudCredentialModal

- Convert SettingsView to 3-tab layout (Preferences/AI/Cloud) matching AdminView pattern
- Extract SettingsPreferencesTab.vue and SettingsAiTab.vue from original SettingsView
- Create SettingsCloudTab.vue with all 4 providers, status badges, action buttons
- Create CloudCredentialModal.vue for WebDAV/Nextcloud credential input
- Handle OAuth callback query params (cloud_connected/cloud_error) in SettingsView.onMounted
- Add success toast (auto-dismiss 5s) and persistent error banner for OAuth results
- Fix pre-existing build failure: add build.target=esnext to vite.config.js for top-level await support
- 2 SettingsCloudTab mount tests passing (W4 — CLAUDE.md)

frontend/src/components/settings/SettingsPreferencesTab.vue

@@ -0,0 +1,65 @@
+<template>
+  <section class="bg-white border border-gray-200 rounded-xl p-6">
+    <h3 class="text-xl font-semibold text-gray-800 mb-2">Document Preferences</h3>
+    <p class="text-sm text-gray-600 mb-4">Choose how PDF documents open when you click on them.</p>
+
+    <div class="space-y-3">
+      <label class="flex items-center gap-3 cursor-pointer">
+        <input
+          type="radio"
+          name="pdf_open_mode"
+          value="in_app"
+          v-model="pdfOpenMode"
+          class="text-indigo-600 focus:ring-indigo-500"
+        />
+        <span class="text-sm text-gray-700">Open documents in-app</span>
+      </label>
+      <label class="flex items-center gap-3 cursor-pointer">
+        <input
+          type="radio"
+          name="pdf_open_mode"
+          value="new_tab"
+          v-model="pdfOpenMode"
+          class="text-indigo-600 focus:ring-indigo-500"
+        />
+        <span class="text-sm text-gray-700">Open documents in new tab</span>
+      </label>
+    </div>
+
+    <!-- Save feedback -->
+    <p v-if="saveFeedback" class="text-xs text-green-600 mt-3">{{ saveFeedback }}</p>
+    <p v-if="saveError" class="text-xs text-red-600 mt-3">{{ saveError }}</p>
+  </section>
+</template>
+
+<script setup>
+import { ref, watch, onMounted } from 'vue'
+import * as api from '../../api/client.js'
+
+const pdfOpenMode = ref('new_tab')
+const saveFeedback = ref('')
+const saveError = ref('')
+let feedbackTimer = null
+
+onMounted(async () => {
+  try {
+    const prefs = await api.getMyPreferences()
+    pdfOpenMode.value = prefs.pdf_open_mode || 'new_tab'
+  } catch {
+    // Default to new_tab if preferences can't be loaded
+  }
+})
+
+watch(pdfOpenMode, async (newValue) => {
+  saveFeedback.value = ''
+  saveError.value = ''
+  clearTimeout(feedbackTimer)
+  try {
+    await api.updateMyPreferences({ pdf_open_mode: newValue })
+    saveFeedback.value = 'Preferences saved.'
+    feedbackTimer = setTimeout(() => { saveFeedback.value = '' }, 3000)
+  } catch (e) {
+    saveError.value = e.message || 'Failed to save preferences.'
+  }
+})
+</script>