fix(windows): hide console windows for media and paste helpers

[stantheman0128]

Summary

On Windows, media pause/resume and paste fallbacks spawn nircmd / PowerShell without windowsHide. That flashes console windows during dictation. runCommand in process.js had the same gap.

This PR passes windowsHide: true for those helper spawns and prefers powershell.exe for media key / GSMTC paths.

AI assistance

Assisted by Cursor / Grok. Human author: Stan Shih (stantheman0128). I reviewed the diff and verification output.

Verification / Evidence

npm run typecheck
# pass

npm run lint
# pass

# Live Win11 smoke:
node -e "const {spawnSync}=require('child_process'); const r=spawnSync('powershell.exe',['-NoProfile','-NonInteractive','-Command','Write-Output HIDE_OK'],{encoding:'utf8',windowsHide:true}); console.log(r.status, r.stdout.trim())"
# 0 HIDE_OK

Test plan

• typecheck + lint
• Live powershell.exe spawn with windowsHide
• Manual: pause media during dictation and confirm no console flash; paste fallback still works