Search: node settings are indexed, with credentials masked on the server

/search gains a `setting` category, `<node>.<setting>` under its flow with the
node type and the value in a new `detail` field, so Ctrl-K finds which node
uses a broker or a timeout and opens the node. `setting_text` is the one place
that decides what may be said: a reference to a stored secret shows its name
(to superusers only, as the secrets list does), a plain value in an `x-secret`
field or under a key like password, token or api_key is masked and never
indexed, nested credentials in headers or query are masked, long values are
clipped. The global search ranks what contains the query as typed ahead of
loose spellings before it caps a group, which long setting values would
otherwise have crowded out.

docs/interface/index.md

@@ -31,9 +31,16 @@ instead: on Home it opens the Control tab, on any other page the assistant.
 
 ### Search
 
-Use **Search**, or ⌘K / Ctrl-K, to find flows, nodes, flow inputs and outputs,
-dashboards, widgets, devices, secrets, modules, workers and alert channels.
-Selecting a result opens its editor or settings.
+Use **Search**, or ⌘K / Ctrl-K, to find flows, nodes, node settings, flow
+inputs and outputs, dashboards, widgets, devices, secrets, modules, workers and
+alert channels. Selecting a result opens its editor or settings.
+
+A setting is listed as `node.setting` with its value beside it, so you can look
+up which node uses a broker, a topic or a timeout. A credential is never shown.
+A setting that points at a stored secret shows only the secret's name, and only to
+superusers. A plain value in a credential field, or under a key such
+as `password`, `token` or `api_key`, shows as `••••` and cannot be searched
+for.
 
 Search covers the current instance. When connected through a portal,
 **All instances** returns to the instance list.