feat(05-10): OAuth fetch + Nextcloud edit fix + Edit on ERROR + text overflow

- client.js: add initiateOAuth() and getConnectionConfig() helpers
- SettingsCloudTab: replace window.location.href with initiateOAuth() + fetch/JWT
- SettingsCloudTab: add Edit button to ACTIVE and ERROR blocks for non-OAuth providers
- SettingsCloudTab: wrap ConfirmBlock in w-full overflow-hidden div
- CloudCredentialModal: add existing prop, edit-mode pre-population via /config endpoint
- CloudCredentialModal: add showAdvanced + customEndpoint for Nextcloud custom paths
- ConfirmBlock: add break-words class to message paragraph
- cloud.py: add GET /api/cloud/connections/{id}/config endpoint (non-secret fields)

frontend/src/components/ui/ConfirmBlock.vue

@@ -1,6 +1,6 @@
 <template>
   <div class="space-y-3">
-    <p class="text-sm text-gray-700">{{ message }}</p>
+    <p class="text-sm text-gray-700 break-words">{{ message }}</p>
     <div class="flex gap-3 items-center">
       <button
         type="button"