feat(open-webui): add image, knowledge and webpage attachments with retry

Extend the AI Chat widget with three ways to ground a conversation:

- Images: attach images to a message, sent inline as OpenAI multimodal
  content parts for vision-capable models. A hint warns when the selected
  model likely has no vision support.
- Knowledge bases: pick RAG collections exposed by /api/v1/knowledge/.
- Web pages: ingest a URL via /api/v1/retrieval/process/web.

Open WebUI does not run RAG from the chat-completions `files` parameter,
so attached collections (web pages and knowledge bases) are grounded by
retrieving the most relevant chunks at send time
(/api/v1/retrieval/query/collection) and injecting them as system context.

Also add a Retry action to re-run the last turn after a model failure, and
handle the paginated `{ items, total }` shape of the knowledge endpoint on
newer Open WebUI versions.

packages/request-handler/src/open-webui.ts

@@ -1,7 +1,12 @@
 import dayjs from "dayjs";
 
 import { createIntegrationAsync } from "@homarr/integrations";
-import type { OpenWebUiChat, OpenWebUiChatListItem, OpenWebUiModel } from "@homarr/integrations/types";
+import type {
+  OpenWebUiChat,
+  OpenWebUiChatListItem,
+  OpenWebUiKnowledge,
+  OpenWebUiModel,
+} from "@homarr/integrations/types";
 
 import { createCachedIntegrationRequestHandler } from "./lib/cached-integration-request-handler";
 
@@ -18,6 +23,19 @@ export const openWebUiModelsRequestHandler = createCachedIntegrationRequestHandl
   queryKey: "openWebUiModels",
 });
 
+export const openWebUiKnowledgeRequestHandler = createCachedIntegrationRequestHandler<
+  OpenWebUiKnowledge[],
+  "openWebUi",
+  Record<string, never>
+>({
+  async requestAsync(integration) {
+    const integrationInstance = await createIntegrationAsync(integration);
+    return await integrationInstance.getKnowledgeAsync();
+  },
+  cacheDuration: dayjs.duration(5, "minutes"),
+  queryKey: "openWebUiKnowledge",
+});
+
 export const openWebUiChatsRequestHandler = createCachedIntegrationRequestHandler<
   OpenWebUiChatListItem[],
   "openWebUi",