fix(cli): use spawnNode for SEA compatibility

[jdalton]

Summary

Replace direct spawn('node', ...) calls with spawnNode() utility to ensure proper Node.js execution in SEA (Single Executable Application) contexts.

Problem

When running from a SEA binary, spawning 'node' directly may not work correctly. The spawnNode() utility handles this by:

• Using system Node.js when available in SEA context
• Falling back to SEA self-spawning with IPC handshake
• Using process.execPath in non-SEA context

Changes

Files Updated

• src/utils/dlx/spawn.mts - spawnCoanaDlx and spawnCdxgenDlx
• src/commands/pip/cmd-pip.mts - Local sfw execution
• src/utils/python/standalone.mts - Local python-cli execution

Pattern

// Before
spawn('node', [scriptPath, ...args], options)

// After
spawnNode([scriptPath, ...args], options)

Benefits

✅ Proper SEA binary support for local tool execution
✅ Automatic system Node.js detection
✅ Fallback to SEA self-spawning when needed
✅ Works correctly in all contexts (SEA, standard Node.js, local binaries)

Test Plan

• Type check passes
• Security checks pass
• Test with SEA binary + local Coana
• Test with SEA binary + local cdxgen
• Test with SEA binary + local sfw
• Test with standard Node.js installation

Impact

Low risk - Only affects local binary execution paths (when SOCKET_CLI_*_LOCAL_PATH is set). Standard dlx paths are unchanged.