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/dict/knowledgebase-dict.ts

@@ -0,0 +1,16 @@
+/**
+ * How a knowledgebase document came in: an uploaded file, or text written
+ * straight into the knowledgebase.
+ */
+export const KnowledgebaseDocumentSources = [
+    { title: "File", value: "file" },
+    { title: "Text", value: "text" },
+] as const;
+
+export type KnowledgebaseDocumentSource = (typeof KnowledgebaseDocumentSources)[number]["value"];
+
+/**
+ * The tools a run gets when it reaches a knowledgebase.
+ */
+export const SearchKnowledgebaseToolName = "search_knowledgebase";
+export const ReadKnowledgebaseDocumentToolName = "read_knowledgebase_document";