Update system root glue scripts for enhanced sys.unixshellcommand/winshellcommand

[jsavin]

Context

Issue #190 adds optional parameters to sys.unixshellcommand and sys.winshellcommand for capturing stderr separately:

sys.unixshellcommand(cmd)                      // Returns stdout string (backward compatible)
sys.unixshellcommand(cmd, @stdout_addr)        // Puts stdout at addr, returns true/false
sys.unixshellcommand(cmd, @stdout_addr, @stderr_addr)  // Both streams, returns true/false

Task

Update any glue scripts in the system root (system.verbs.* etc.) that wrap or provide utilities for these shell command verbs to account for the new optional parameters.

This includes:

• Any wrapper verbs that call sys.unixshellcommand or sys.winshellcommand
• Documentation/examples in system tables
• Any verb binding glue code that exposes these

Acceptance Criteria

• All shell command verb usages in system root are compatible with new API
• New optional parameter capabilities are exposed/documented in system tables
• Backward compatibility maintained for existing code

Related

• Issue sys.unixshellcommand/winshellcommand/macshellcommand: Add optional stderr parameter #190 (sys shell commands with optional stderr)
• Planning: Phase 3 CLI completion