feat(maestro): add maestro send for typing into a session

Adds POST /api/sessions/:id/input and a CLI command on top of it, so a
script (or another agent) can hand an instruction to a running session
without attaching to it.

The text goes in as one write and the Enter follows 150ms later: agents
that run a full-screen prompt coalesce a burst of input into a paste, and
a newline inside that burst becomes a line break instead of sending the
message. `--no-enter` skips the Enter and leaves the text in the prompt.

The session argument takes an ID, a unique ID prefix, or a session name;
names win over prefixes. A session whose pane has exited is refused (409)
rather than silently accepted — unlike a stray keystroke on an attach
socket, a send that goes nowhere is worth hearing about.

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

CLAUDE.md

@@ -11,6 +11,7 @@ persistence, WebSocket for transport.
 maestro daemon            tmux wrapper + session API on 127.0.0.1:7070
   ├── GET/POST /api/sessions        list / spawn
   ├── DELETE   /api/sessions/:id    kill
+  ├── POST     /api/sessions/:id/input  type text into a session
   ├── GET      /api/info            hostname, version, home dir, spawn presets
   ├── GET      /api/dirs            directory listing (spawn autocomplete)
   ├── GET      /api/recent-dirs     spawn history
@@ -18,7 +19,7 @@ maestro daemon            tmux wrapper + session API on 127.0.0.1:7070
   ├── WS       /api/events          Snapshot + session deltas
   └── WS       /api/attach/:id      raw PTY bytes
 
-maestro list/spawn/attach/kill      CLI client
+maestro list/spawn/attach/kill/send  CLI client
 maestro tui                         ratatui client
 maestro-web                         serves the SPA, reverse-proxies /api/* to the daemon
 ```