fix(maestro): leader twice sends one literal leader byte

ctrl-a is consumed as the leader on every press, so it never reaches the
shell and readline's beginning-of-line was gone with no way back — unlike
Ctrl-K, which already has an escape hatch. Fix it the way tmux does:
pressing the leader twice sends the literal leader byte to the focused
pane and clears the pending chord, on both web and TUI, built from the
configured leader so a rebound leader carries it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/COMMAND-BAR.md

@@ -45,8 +45,15 @@ mirroring the TUI's. `ctrl-a` is select-all in a browser; the web
 `preventDefault`s it, since selecting all of a terminal pane does nothing
 useful.
 
-Only Ctrl-K gets an escape hatch. No other control character is intercepted, so
-none of them needs one.
+The leader itself needs the same kind of way back: holding it consumes every
+press, on both clients, even before anything is bound behind it. Pressing it
+twice — `ctrl-a ctrl-a` by default — sends one literal leader byte to the
+focused pane and clears the pending chord, the way tmux resolves a doubled
+prefix key. This chord is also built from the configured leader, so a
+rebound leader carries its own escape hatch with it.
+
+Only Ctrl-K and the leader itself get an escape hatch. No other control
+character is intercepted, so none of them needs one.
 
 ### Focus round-trip