fix(skill): harden Windows updates and path handling

[gujieye]

Summary

• fall back to an in-place, rollback-capable skill directory reconciliation when Windows blocks the canonical directory rename with EPERM or EBUSY
• reject skill packages whose projected canonical or agent-visible paths exceed the legacy Windows MAX_PATH limit before replacing the existing installation
• apply the same locked-directory and long-path protections to the standalone wiki postinstall flow
• add regression coverage for locked-directory updates, stale-file cleanup, and pre-swap long-path rejection

Behavior

For bailian-docs-llm-wiki, this change prevents an overlong package from being linked into an agent and breaking that agent's complete skill-library traversal. The package itself still needs to shorten its generated paths before it can be installed and used on Windows systems without long-path support.

Fixes #225.
Mitigates #224 on the CLI side.

Validation

• pnpm exec vp check — passed with 0 errors; 3 pre-existing warnings remain
• pnpm exec vp test packages/core/tests/skills-installer.test.ts packages/commands/tests/e2e/skill.e2e.test.ts — 35 tests passed
• pnpm exec vp run -r build — passed
• full recursive test run: 441 tests passed; 10 existing agent-detection tests failed because the test environment exposes /etc/codex outside the isolated HOME