fix(worktree): make checkout timeout configurable

[bold84]

Summary

• Make worktree checkout time configurable through worktreeTimeoutSeconds in global/project subagents.json.
• Add an auto strategy that scales from tracked file count (60-second floor, 5 ms per tracked file, 30-minute cap) plus bounded fixed values from 30 to 3600 seconds.
• Expose the setting through /agents -> Settings -> Worktree timeout.
• Clean up partial worktrees after failed or timed-out checkout attempts and terminate the Git process tree on Windows when possible.
• Use git rev-parse --show-prefix for subdirectory mapping so Windows 8.3 and long path forms do not produce an incorrect workPath.

Motivation

The previous implementation used a hardcoded 30-second execFileSync timeout. On a Windows repository with approximately 85,550 tracked files, checkout exceeded that limit and surfaced the generic “not a git repo / no commits / git worktree add failed” error. The timed-out checkout could also leave a locked partial worktree behind.

Validation

• npm run typecheck
• npm run lint
• npm run build
• npm test -- test/settings.test.ts test/worktree.test.ts — 79 tests passed

The complete suite was also run on Windows. 42 files passed; the remaining failures are existing environment-sensitive tests that assume POSIX path formatting or an empty global custom-agent directory.