fix(mcp-client): add child.deinit() in spawn error path (#166)

When child.spawn() fails, the child process resources were leaking.
Added child.deinit() call before the early return to properly clean up.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Trinity Agent

src/tri-api/mcp_client.zig

@@ -57,6 +57,7 @@ pub const McpManager = struct {
 
         child.spawn() catch |err| {
             std.debug.print("[mcp] Failed to spawn {s}: {s}\n", .{ name, @errorName(err) });
+            child.deinit();
             return 0;
         };