fix: stop hanging project typechecks

[christopher-buss]

Description

Closes #9494 - vitest run hanging after successful project typechecking and leaving an orphaned tsc or tsgo --watch process.

Project configs previously resolved watch from configDefaults instead of inheriting the root configuration. In an interactive terminal, this produced watch: false at the root but watch: true in the project, causing the typechecker to start in watch mode during vitest run.

This PR:

• propagates the root watch value to project configs
• destroys the typechecker output streams during shutdown
• terminates the complete process tree on Windows
• uses a detached process group for tree termination on other platforms
• adds regression coverage for project configuration and process cleanup

The terminal-specific behavior was also verified using a forced interactive-terminal reproduction. After the fix, both root and project resolve watch: false, Vitest exits normally, and no watched typechecker process remains.

AI-assisted by Codex and reviewed using Claude Opus + a human (myself)!

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