feat: pass --name to local claude spawns so workers carry their session names as peer names

Version-gated fail-closed at 2.1.224 (the cross-session-messaging release,
flag presence verified against that binary): an unknown or older CLI yields
a spawn command byte-identical to before, because claude aborts startup on
an unknown option and that would kill every session spawn. The value is
allowlist-sanitized ahead of the double-quoted interpolation, and only the
local command carries the flag; docker/remote builders never see it since
their CLI is not the probed binary. Verified E2E on an isolated instance:
cmdline shows --name, ListAgents lists the session name, replies arrive
tagged from-name.

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

src/mux-interface.ts

@@ -97,6 +97,8 @@ export interface RespawnPaneOptions {
   sessionId: string;
   workingDir: string;
   mode: SessionMode;
+  /** Session display name; a respawned claude keeps its `--name` peer name (version-gated, local only). */
+  name?: string;
   niceConfig?: NiceConfig;
   model?: string;
   claudeMode?: ClaudeMode;