fix(filesystem): normalize paths for glob matching

[go165]

Summary

• normalize filesystem search relative paths to POSIX separators before minimatch evaluation
• keep returned search results unchanged as full filesystem paths
• add a regression test for Windows-style relative paths matching slash-based glob patterns

Fixes #3517

Validation

• npm exec --workspace src/filesystem -- vitest run tests/lib.test.ts --coverage=false
• git diff --check

Blocked local checks:

• npm test --workspace src/filesystem: the target lib suite passed, but the full package test run also invokes startup/structured-content tests that require dist/index.js and workspace SDK resolution in this fresh worktree.
• npm run build --workspace src/filesystem: blocked in this fresh worktree because @modelcontextprotocol/sdk workspace dependencies are not installed/resolved locally. I used the existing dependency checkout only for the targeted lib test and did not reinstall the full workspace.