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/harness/tools/bot/extensions/list-extensions-tool.ts

@@ -25,7 +25,7 @@ type Params = {
 };
 
 type Args = {
-    kind?: ExtensionKind;
+    kind?: z.infer<typeof ExtensionKindSchema>;
     id?: number;
     query?: string;
 };
@@ -58,7 +58,7 @@ export default function listExtensionsTool({ user_id }: Params): HarnessTool<Arg
     };
 }
 
-async function describeOne({ kind, id }: { kind: ExtensionKind; id: number }) {
+async function describeOne({ kind, id }: { kind: Exclude<ExtensionKind, "knowledgebase">; id: number }) {
     const access = (await grabExtensionAccess({ kind }))(id);
 
     if (kind == "skill") return describeExtension({ kind, item: await grabSkill({ skill_id: id }), ...access, full: true });