Rewrite DeskDesk to consume the pluggable integration registry (drop the bespoke knowledge tab + knowledge_article schema) #5

Background

DeskDesk currently surfaces "knowledge articles" via a bespoke path:

• src/views/KnowledgeTab.vue — a hand-rolled sidebar tab
• a knowledge_article schema in lib/Settings/deskdesk_register.json (+ references in lib/Service/SettingsService.php, src/store/modules/{object,settings}.js, src/store/store.js)
• a "sync" placeholder

OpenRegister now ships a pluggable integration registry (umbrella pluggable-integration-registry, ADR-019) with an XWiki "Articles" leaf (openregister #1493 backend, nextcloud-vue #213 frontend). DeskDesk should drop the bespoke path and consume the registry instead — that's the whole point of building the leaf.

What "consume the registry" means here

1. src/main.js — after the lib CSS import, install the registry shim + register the providers:

   import { installIntegrationRegistry, registerBuiltinIntegrations, registerXwikiIntegration } from '@conduction/nextcloud-vue'
   installIntegrationRegistry()
   registerBuiltinIntegrations()       // files / notes / tags / tasks / audit-trail
   registerXwikiIntegration()          // the "Articles" (XWiki) leaf

2. manifest.json — for the desks-detail page, replace config.sidebar.tabs: [...] (the bespoke data/knowledge/metadata set) with config.sidebar: { useRegistry: true } (optionally excludeIntegrations: [...]). This needs nextcloud-vue #218 (CnDetailPage.sidebar now accepts useRegistry and pushes it through objectSidebarState).
3. src/App.vue — the #sidebar-slot <CnObjectSidebar> must bind the two new state fields so the manifest value takes effect:

   :use-registry="objectSidebarState.useRegistry"
   :exclude-integrations="objectSidebarState.excludeIntegrations"

   (alongside the :tabs / :hidden-tabs / :register / :schema it already binds). Drop the KnowledgeTab import + the customComponents['knowledge-tab'] entry.
4. Backend — remove the knowledge_article schema from lib/Settings/deskdesk_register.json and the references in SettingsService.php / the stores. Articles now come from the xwiki integration (an OpenConnector xwiki source — see openregister/docs/Integrations/xwiki.md + docs/Integrations/xwiki-openconnector-source.yaml), not a DeskDesk-local schema + sync.
5. src/views/KnowledgeTab.vue — delete (replaced by CnXwikiTab from the registry).

Also: a bug to fix while we're in there

While live-testing the rewrite, the desks-detail page logged:

TypeError: Cannot read properties of undefined (reading '@self')

in DeskDesk's detail render path (one of the wrappers — DetailPageWrapper.vue or a store module reading object['@self'] before the object is loaded). Reproduce by opening /apps/deskdesk/desks/:id; needs a null-guard / loading-state check.

Then: Part 4 of the tutorial

Once the rewrite works end-to-end (XWiki source configured, Articles tab populated), rewrite the Part 4 MDX tutorial — "wire DeskDesk's knowledge surface to an external XWiki via the integration registry" — with real screenshots of the Articles tab + the detail-page preview. (Keep the current wrong-shape Part 4 until then.)

Depends on

• openregister: umbrella #1307 + the integration-xwiki leaf #1493 — merged
• @conduction/nextcloud-vue: #202 → #204 → #209 → #210 → #213 (registry + widgets + xWiki tab/card) + #218 (CnDetailPage manifest useRegistry) — merged

Cleanest done after those stacks land on development / beta.