feat(maestro): serve the configured leader to the web client

The TUI read its leader from `[tui].leader`; the web used `DEFAULT_LEADER`,
a module constant. Rebinding one left the other on `ctrl-a`, so the two
escape hatches hanging off the leader (`leader ctrl-k`, `leader leader`)
moved on one client and not the other.

`GET /api/info` now carries `leader`. The web binds that when it arrives and
rebuilds the leader-owning `CommandSet`, so the `?` overlay and the command
bar render the configured chord; an absent or empty field — an older daemon,
or an unreachable `/api/info` — leaves it on `ctrl-a`.

Chose the existing `[tui].leader` served as-is over a new shared key: one
knob, no precedence rules between two spellings, and no migration for
operators who already set it. The name is a wart — it is the leader for every
client now, not the TUI's — and `docs/COMMAND-BAR.md` and `docs/INSTALL.md`
say so.

docs/COMMAND-BAR.md

@@ -45,6 +45,12 @@ 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.
 
+One knob drives both clients: the daemon serves `[tui].leader` as `leader` on
+`GET /api/info`, and the web binds that instead of its own constant (#159). A
+daemon too old to send the field, or an unreachable `/api/info`, leaves the web
+on `ctrl-a`. The section is named `[tui]` for history — it is the leader for
+every client, not the TUI's alone.
+
 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

docs/INSTALL.md

@@ -136,7 +136,8 @@ cover every v1 action — only override what you want to change:
 ```toml
 [tui]
 theme = "dark"              # see the theme list below
-leader = "ctrl-a"            # one byte that escapes Insert mode
+leader = "ctrl-a"            # one byte that escapes Insert mode; the web reads
+                             # the same setting off /api/info
 chord_timeout_ms = 1000      # how long to hold a partial chord like `ctrl-w`
 
 [tui.keymap.normal]