feat: the right pane describes what's selected in the pane you're in

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/keys.md

@@ -105,6 +105,13 @@ anything loads.
 
 ## Layout
 
+The pane on the right describes what's selected in the pane you're in: the
+account or subscription in Sources, the vault in Vaults, the secret in
+Secrets. Going into it (`4`, or `tab` from an account's row) keeps it on
+that; there `j`/`k`, `/` and `y` work on its rows, and `shift+tab` goes
+back. A value you reveal stays in view whichever pane you're in, until
+it's hidden.
+
 | Key | Action |
 |---|---|
 | `ctrl+←`/`ctrl+→` or `<`/`>` | move the divider between the left panes and the detail pane |