fix(cli): hide detached Windows spawns

[kvnloo]

Summary

• pass windowsHide: true to telemetry exit flush, custom browser launch, and background preview detached spawns
• cover each real spawn path with a behavior regression test
• match the existing auto-update spawn behavior

Fixes #3476

Verification

• bun run --filter @hyperframes/cli test -- src/telemetry/client.test.ts src/utils/openBrowser.test.ts src/commands/previewLifecycle.test.ts (61 passed)
• bun run --filter @hyperframes/cli typecheck
• bun run lint
• bun run format:check
• bun run build
• git diff --check
• sabotage check: removing windowsHide from openBrowser made its new regression test fail

The full bun run test is not clean in this environment. Studio has 97 failures caused primarily by unavailable localStorage, and the full CLI run has 3 unrelated skillsManifest.test.ts lock-pruning failures. The focused tests for all changed paths pass.

Windows real-device validation has not been performed.

Scope

This does not change ffmpeg handling from #3379 or chrome-headless-shell handling from #3430. It does not add a shared spawn helper or lint rule.

AI assistance

Implemented and verified with Hermes Agent using Codex. I reviewed the resulting diff and test evidence.

[Bortlesboat]

Checked 89205665b1a70cea061c43705ffb44b234655ab1 on native Windows with Node 24.14.0 and Bun 1.3.14. All 61 focused tests pass: 55 across previewLifecycle.test.ts and openBrowser.test.ts, plus six in telemetry/client.test.ts. Oxlint and oxfmt also pass for all six changed files.

For a fresh checkout, the telemetry suite needs the parser/lint packages and core's generated runtime modules first. After building @hyperframes/parsers, @hyperframes/lint, and @hyperframes/core, it collects and passes without source edits. The initial missing-module errors were checkout preparation, not failures of this patch.

I checked all three modified spawn paths: the added option retains their detached behavior, stdio routing, and existing unref() calls, and the preview injection type includes the new option. No issue found within this change.

This supplies Windows test/build evidence, but the focused tests mock process spawning. Actual visible console behavior when launching a real preview or browser remains unverified; I did not repeat the full monorepo suite.

[miga-heygen]

Closing — stale draft PR. Please reopen if still relevant.