feat(open-webui): full attachment menu with all source types

Replace the single attach popover with an Open WebUI-style multi-level
menu covering every attachment source:

- Upload Files: images stay inline (vision); other files are uploaded and
  grounded via retrieval (`file-{id}` collection).
- Capture: take a photo from the webcam as an inline image.
- Attach Webpage: ingest a URL (existing).
- Attach Files: pick files already stored in Open WebUI.
- Attach Notes: inject the contents of a note as context.
- Attach Knowledge: nested picker with checkboxes, expandable to a base's
  files (replaces the flat checkbox list).
- Reference Chats: bring a previous conversation in as context.

Knowledge bases, web pages and files are grounded by retrieval; notes and
referenced chats are injected verbatim as context blocks. Adds the
supporting integration methods (list files/notes, knowledge files, upload
file), request handlers and tRPC procedures.

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

@@ -4,8 +4,10 @@ import { createIntegrationAsync } from "@homarr/integrations";
 import type {
   OpenWebUiChat,
   OpenWebUiChatListItem,
+  OpenWebUiFileSummary,
   OpenWebUiKnowledge,
   OpenWebUiModel,
+  OpenWebUiNote,
 } from "@homarr/integrations/types";
 
 import { createCachedIntegrationRequestHandler } from "./lib/cached-integration-request-handler";
@@ -36,6 +38,45 @@ export const openWebUiKnowledgeRequestHandler = createCachedIntegrationRequestHa
   queryKey: "openWebUiKnowledge",
 });
 
+export const openWebUiKnowledgeFilesRequestHandler = createCachedIntegrationRequestHandler<
+  OpenWebUiFileSummary[],
+  "openWebUi",
+  { knowledgeId: string }
+>({
+  async requestAsync(integration, input) {
+    const integrationInstance = await createIntegrationAsync(integration);
+    return await integrationInstance.getKnowledgeFilesAsync(input.knowledgeId);
+  },
+  cacheDuration: dayjs.duration(1, "minute"),
+  queryKey: "openWebUiKnowledgeFiles",
+});
+
+export const openWebUiFilesRequestHandler = createCachedIntegrationRequestHandler<
+  OpenWebUiFileSummary[],
+  "openWebUi",
+  Record<string, never>
+>({
+  async requestAsync(integration) {
+    const integrationInstance = await createIntegrationAsync(integration);
+    return await integrationInstance.listFilesAsync();
+  },
+  cacheDuration: dayjs.duration(30, "seconds"),
+  queryKey: "openWebUiFiles",
+});
+
+export const openWebUiNotesRequestHandler = createCachedIntegrationRequestHandler<
+  OpenWebUiNote[],
+  "openWebUi",
+  Record<string, never>
+>({
+  async requestAsync(integration) {
+    const integrationInstance = await createIntegrationAsync(integration);
+    return await integrationInstance.listNotesAsync();
+  },
+  cacheDuration: dayjs.duration(30, "seconds"),
+  queryKey: "openWebUiNotes",
+});
+
 export const openWebUiChatsRequestHandler = createCachedIntegrationRequestHandler<
   OpenWebUiChatListItem[],
   "openWebUi",