fix(maestro): align TUI and web shortcuts

Spawn was `s`/`S` in the TUI and `n`/`N` in the web client; the TUI now
uses `n`/`N` too. The web sidebar gains `c`, `r` and `x` — collapse,
rename, kill — which the TUI already bound.

docs/SIDEBAR.md now carries the shared table, so a new binding has one
place to land on both clients.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/SIDEBAR.md

@@ -274,3 +274,21 @@ than jumping to the end of the list.
 The web client needs a chord to reach the list at all (`Ctrl+Shift+H`, and the
 same chord back): an attached terminal owns every plain keystroke. The TUI uses
 `ctrl-w h`.
+
+Everything else is the same key on both clients:
+
+| key     | action                                      |
+|---------|---------------------------------------------|
+| `j`/`k` | move the highlight (arrows too)             |
+| `Enter` | open the session, or expand the folder      |
+| `Tab`   | hand the keyboard to the pane               |
+| `c`     | collapse or expand the highlighted folder   |
+| `r`     | rename the highlighted session              |
+| `x`     | kill the highlighted session                |
+| `n`     | open the spawn form                         |
+| `N`     | spawn with every default resolved           |
+| `?`     | show the shortcut overlay                   |
+
+The TUI binds these through its keymap, so a user can rebind any of them; the
+web client's are fixed. A binding added to one client belongs in this table and
+in both help overlays.