fix(bash): link executed scripts across files

[balloon72]

Summary

Link Bash scripts that execute sibling scripts directly or through a common shell runner.

Root cause

The Bash extractor only treated source and . as cross-file commands. Direct ./script.sh calls and commands such as bash ./script.sh were ignored, leaving script call topology disconnected.

Changes

• Emit extracted calls edges from the current entrypoint or function to the target script entrypoint.
• Resolve literal .sh paths for direct execution and bash, sh, zsh, ksh, and dash runners.
• Skip dynamic, missing, and user-function-shadowed invocations.
• Cover absolute and relative inputs with regression tests.

Validation

• python -m pytest tests/test_extract.py -k "script_invocation" -q (6 passed)
• python -m pytest tests/test_extract.py -q -k "not collect_files_follows_symlinked_directory and not collect_files_skips_out_of_root_symlinked_directory and not collect_files_skips_out_of_root_symlinked_file_by_default and not collect_files_handles_circular_symlinks" (119 passed, 1 skipped)
• python -m py_compile graphify/extractors/bash.py tests/test_extract.py
• python -m graphify update .
• git diff --check origin/v8...HEAD

The full local suite was attempted but could not complete because Windows Store Python repeatedly crashed in existing ProcessPoolExecutor pipeline tests. GitHub CI remains the full-suite check.

Fixes #1756