fix(native-engine): suppress Windows console window when spawning phase-server

[matthewevans]

The desktop shell is a GUI-subsystem app but phase-server.exe is
console-subsystem, so Windows allocated a visible console window for the
child on every launch. Apply the CREATE_NO_WINDOW creation flag on all
three Windows console spawns: the phase-server launch (the persistent
window), plus the tasklist stale-process probe and taskkill cleanup
(each of which briefly flashed its own console).

Summary by CodeRabbit

• Bug Fixes
  • Prevented unwanted console windows from appearing when starting and stopping the native service on Windows.
  • Improved the background process experience during shutdown and process checks without changing existing functionality.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 6895ca3 and c29fce1.

📒 Files selected for processing (1)

• client/src-tauri/src/native_engine.rs

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📝 Walkthrough

Walkthrough

Windows process creation is updated to suppress console windows for the native phase-server, shutdown taskkill, and identity-check tasklist commands while preserving existing arguments, environment, and error handling.

Changes

Windows process console suppression

Layer / File(s)	Summary
Apply Windows no-window flags client/src-tauri/src/native_engine.rs	Adds the Windows command extension and CREATE_NO_WINDOW, refactors server command construction to apply the flag before spawning, and applies it to Windows taskkill and tasklist invocations.

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: suppressing the Windows console window for native-engine process spawning.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ship/suppress-windows-console-window

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