herdr phase 2: Live Pane tab (xterm.js → node's herdr TUI)

The killer UX feature: click a mission's Live Pane tab and watch the
actual Herdr TUI on the target node in the browser — cursor, colors,
tool output, all live. WebRTC DataChannel direct where the browser
can reach the node peer-to-peer, WS-relayed fallback otherwise
(same auto-negotiation the INFRA node terminal already uses).

Zero new deployment infra — reuses the existing terminal_ticket +
terminal_ws + PTY-over-control-channel machinery. The one primitive
we grew: PtyTarget::Command variant so the node can spawn an
arbitrary program (\`herdr\`) in the PTY instead of the login shell.

Node daemon (clawmates-node):
  - PtyTarget grows a Command { argv } variant
  - spawn_command_pty resolves bare names against user + system bin
    dirs (matches how tool_update finds claude/kimi)
  - PtyTarget::from_frame reads the `command` array from the pty_open
    frame; precedence Command > Container > Host

cm-api:
  - NodeHub::open_pty grows an optional command argv; when set, the
    frame carries it and the daemon spawns the program directly.
  - routes::nodes::TermCtrl gains a `command: Vec<String>`; the
    fallback branch threads it through.

Frontend:
  - core.ts::webrtcConnector takes an optional commandOverride
    that ships inside the fallback frame
  - nodeHerdrConnector(nodeId) — mints the standard ticket + WS URL
    but overrides command to ["herdr"]
  - MissionCanvas grows a "pane" tab, visible only when
    runtime_kind='local_herdr'. LivePane subcomponent uses xterm.js
    (already a workspace dep) via useResilientTerminal, shows a
    connecting/relayed/direct pill in the corner.

To watch a mission live: pick "On a fleet node (Herdr)" + target
node in the wizard, launch, click Pane tab → node's Herdr TUI
appears. Navigate to the mission workspace in the Herdr sidebar
(mouse or prefix+w) to zoom into the mission's pane.

Focus-a-specific-pane-directly is a later enhancement — Herdr has
no CLI arg for it yet, so operator navigates the sidebar for now.

Verified: cargo check --workspace + tsc --noEmit both green.

crates/cm-api/src/routes/nodes.rs

@@ -293,6 +293,10 @@ struct TermCtrl {
     candidate: Option<String>,
     sdp_mid: Option<String>,
     sdp_mline_index: Option<u16>,
+    /// When present on `fallback`, spawns this argv in the PTY instead of
+    /// the login shell (used by the Herdr Live Pane).
+    #[serde(default)]
+    command: Vec<String>,
 }
 
 /// The terminal WS is BOTH the WebRTC signaling channel and the fallback data
@@ -335,8 +339,15 @@ async fn bridge_terminal(hub: Arc<NodeHub>, node_id: NodeId, socket: WebSocket)
                     let rows = c.rows.unwrap_or(24);
                     match c.kind.as_str() {
                         "resize" => hub.terminal_resize(node_id, sid, cols, rows).await,
-                        // Host shell (no container) — the Infra node terminal.
-                        "fallback" => hub.open_pty(node_id, sid, cols, rows, None, None).await,
+                        // Host shell by default; `command` override wins.
+                        "fallback" => {
+                            let cmd = if c.command.is_empty() {
+                                None
+                            } else {
+                                Some(c.command.as_slice())
+                            };
+                            hub.open_pty(node_id, sid, cols, rows, None, None, cmd).await
+                        }
                         "webrtc_offer" => {
                             hub.webrtc_offer(
                                 node_id,