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>

crates/maestro-cli/src/dispatch.rs

@@ -10,7 +10,7 @@ use maestro_protocol::DaemonClient;
 
 use crate::attach::{parse_detach_key, run_attach_url};
 use crate::cli::Command;
-use crate::sessions::{run_kill, run_list, run_spawn};
+use crate::sessions::{run_kill, run_list, run_send, run_spawn};
 use maestro_config::{default_config_path, MaestroConfigFile};
 
 #[derive(Debug, thiserror::Error)]
@@ -24,6 +24,10 @@ pub enum CliError {
     Attach(#[from] crate::attach::AttachError),
     #[error("{0}")]
     Hooks(#[from] maestro_hooks::HooksError),
+    #[error("{0}")]
+    Resolve(#[from] crate::sessions::ResolveError),
+    #[error("nothing to send: pass the text as arguments or pipe it on stdin")]
+    NothingToSend,
     #[error("could not determine the home directory ($HOME unset?)")]
     NoHome,
     #[error("{0}")]
@@ -82,6 +86,10 @@ pub async fn dispatch(
             run_kill(&daemon, &args).await?;
             println!("killed {}", args.session_id);
         }
+        Command::Send(args) => {
+            let id = run_send(&daemon, &args, &mut std::io::stdin()).await?;
+            println!("sent to {id}");
+        }
         Command::Hooks(_) => unreachable!("hooks handled before the daemon client exists"),
     }
     Ok(())