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/utils/extension-state-note.ts

@@ -0,0 +1,21 @@
+import type { BotExtension } from "@/src/types";
+
+type Params = {
+    item: Pick<BotExtension, "kind" | "state" | "enabled">;
+};
+
+/**
+ * What an extension's row says about whether it works: off, not working,
+ * not checked yet, or nothing when it's fine. A skill has nothing to
+ * connect or run, so it never reports a failure; a knowledgebase reports a
+ * document it couldn't read.
+ */
+export default function extensionStateNote({ item }: Params) {
+    if (!item.enabled) return "Off for every bot";
+    if (item.kind == "skill") return "";
+    if (item.kind == "knowledgebase") return item.state == "error" ? "A document couldn't be read" : "";
+    if (item.state == "error") return "Not working";
+    if (item.state == "untested") return "Not checked yet";
+
+    return "";
+}