Fix VS Code Remote-WSL project root detection (issue #1032)

[daniel-vincent-veriforce]

What / Why / How

Fixes #1032.

When VS Code is launched from a shortcut on Windows and opens a remote WSL workspace, VSCODE_CWD can point to the local VS Code installation directory rather than the remote workspace. The VS Code Copilot adapter previously trusted that value and anchored project-boundary checks to the install directory, rejecting legitimate remote file reads.

This change:

• Adds isVSCodeInstallPath() with cross-platform separator support for stable/Insiders Windows, macOS, and Linux install locations.
• Keeps CLAUDE_PROJECT_DIR as the highest-priority value.
• Skips an install-directory VSCODE_CWD and falls through to process.cwd().
• Adds unit coverage for install-path detection and the adapter cascade.
• Hardens the existing standalone fatal-exit test timeout for slow WSL startup.

All paths and user names in the issue and tests are anonymized.

Affected platforms

• Claude Code
• Cursor
• VS Code Copilot (GitHub Copilot)
• JetBrains Copilot
• Gemini CLI
• Qwen Code
• OpenCode
• KiloCode
• Codex CLI
• OpenClaw (Pi Agent)
• Pi
• Kiro
• Antigravity
• Zed
• All platforms

Test plan

• Focused Vitest: utility, VS Code adapter, and lifecycle tests — 67 passed.
• npm run typecheck — passed.
• Build, bundle assertions, and asymmetric-drift assertions — passed.
• Full npm test — 4,703 passed, 44 skipped.

The lifecycle test-only timeout change addresses slow standalone bundle startup under WSL; no production lifecycle behavior was changed.

Checklist

• Tests added/updated (TDD: red → green)
• npm test passes
• npm run typecheck passes
• Docs updated if needed
• No Windows path regressions (forward slashes only)
• Targets next branch