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/knowledgebases/locate-passage.ts

@@ -0,0 +1,31 @@
+type Params = {
+    /**
+     * The document's whole text.
+     */
+    text: string;
+    /**
+     * One of its passages, which may start with a heading carried over and
+     * a stretch repeated from the passage before.
+     */
+    passage: string;
+};
+
+/**
+ * Where a passage sits in its document, roughly: found by its last line
+ * (the part least likely to be a carried heading or an overlap), counted
+ * back by where that line sits in the passage. 0 when it can't be found.
+ */
+export default function locatePassage({ text, passage }: Params) {
+    const lines = passage.split("\n").map((line) => line.trim()).filter(Boolean);
+
+    for (let i = lines.length - 1; i >= 0; i--) {
+        const line = lines[i]!;
+        const at = text.indexOf(line);
+
+        if (at < 0) continue;
+
+        return Math.max(0, at - passage.lastIndexOf(line));
+    }
+
+    return 0;
+}