Add knowledgebases

Knowledgebases give bots RAG over documents, scoped like extensions: to
particular bots, to a workspace, or to every bot, with their own button
beside Tools in the composer. Documents are chunked and embedded by the
file-ingest worker with the install's embedding model, which is now an
install-wide setting rather than a per-bot one.

- Word search runs on an FTS5 index ranked by BM25, with a scored LIKE
  fallback for scripts written without spaces.
- Changing the embedding model re-indexes documents automatically.
- Ingest jobs wait without spending attempts while every embedding model
  rests, fail at once on errors retrying can't fix, and keep passages
  searchable by words when the model refuses.
- Settings > Knowledgebases shows each knowledgebase's and document's
  index state: spinner, warning, grey check (words only) or green check.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/components/general/extension-icon.tsx

@@ -1,12 +1,14 @@
-import { BookOpen, Plug, Wrench } from "lucide-react";
+import { BookOpen, Library, Plug, Wrench } from "lucide-react";
 import type { BotExtension } from "@/src/types";
 
 /**
- * The icon of an MCP server (a plug), a tool (a wrench) or a skill (a book).
+ * The icon of an MCP server (a plug), a tool (a wrench), a skill (a book)
+ * or a knowledgebase (a library).
  */
 export default function extensionIcon({ kind }: { kind: BotExtension["kind"] }) {
     if (kind == "mcp") return Plug;
     if (kind == "skill") return BookOpen;
+    if (kind == "knowledgebase") return Library;
 
     return Wrench;
 }