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/functions/backend/db/bot-files/ingest-bot-file.ts

@@ -166,6 +166,12 @@ export default async function ingestBotFile({
 
         return { status: "ingested", chunks: embedded };
     } catch (error) {
+        /**
+         * Every model resting means nothing was tried: the job waits for
+         * them, and the file keeps whatever it said before.
+         */
+        if (error instanceof HarnessError && error.resting) throw error;
+
         const message = error instanceof Error ? error.message : String(error);
 
         await BunSQLite.sql({