fix: hide child process windows on Windows

[haosenwang1018]

Summary

• add windowsHide: true to the detached watcher fork() path
• add windowsHide: true to the watcher child spawn path
• add windowsHide: true to the agent task executor and Claude task runner spawn paths

Why

Issue #459 reports that zeroshot spawns visible console windows for child Node.js processes on Windows.

Node's spawn() / fork() create those windows by default on Windows unless windowsHide: true is set. Since zeroshot launches background watcher/task processes, those extra consoles are just UI noise and make the tool feel broken in desktop use.

Testing

• ./node_modules/.bin/mocha tests/providers/detection.test.js
• manually verified the four Windows-related spawn/fork call sites now all set windowsHide: true

Fixes #459

[tomdps]

Status review (2026-07-29):

• Windows-support theme: this addresses Windows: spawned Node.js processes create visible console windows (fix: windowsHide: true) #459’s visible child console windows and belongs with the Windows process-management/provider-detection cluster.
• Current main already sets windowsHide: true in src/claude-task-runner.js (_spawnAndGetTaskId), src/agent/agent-task-executor.js (spawnTaskProcess), task-lib/runner.js (spawnWatcher), and task-lib/watcher.js; lib/provider-detection.js also uses where on win32.
• This PR currently conflicts with main and has no reported checks; its functional changes have been superseded, so it is not merge-ready as submitted.