fix(tail): handle zero line counts - #1271

tail({ '-n': 0 }, file) currently returns the whole file, while tail('-n', 0, file) reports no paths. Handle a zero count after validating the file arguments, preserving file errors. Also make +0 start at the first line, consistent with native tail.

Add regressions for both option forms, multiple files, piped input, and missing files.

Validation: npm test passes on Node 20, 24, and 26 (631 passed, 6 existing skips). Coverage, lint, and the Node support check pass. An additional 36 cases match native tail output.