fix: resolve bash sources for extensionless libs and bare names

[Souptik96]

Fixes #2171

Both gaps confirmed against v8 (0.9.26) and fixed along the directions in the issue.

1. Extensionless shebang scripts

_SHEBANG_DISPATCH routes a #!/usr/bin/env bash file with no extension to
extract_bash, so its functions are indexed — but the cross-file source pass picked
participants by filename suffix:

sh_paths = [p for p in paths if p.suffix in (".sh", ".bash")]

so a sourced extensionless lib was excluded and calls into it never bound.

Now selected by shape as well: the bash extractor tags every node it emits with
metadata.language == "bash". I kept the suffix check alongside it so an empty .sh file
— which has no nodes to inspect — still participates.

2. Bare source lib.sh

Only the raw.startswith((".", "/")) branch recorded a bash_sources entry; a bare name
fell through to the opaque imports fallback, so neither the source edge nor calls into the
lib resolved. The else branch now binds a sibling of that name when one exists.

The existence gate from the ./-prefixed branch carries over, so this stays a miss-fix and
not a fabrication: a bare name resolving to no sibling keeps the old imports edge and
records no bash_sources entry. is_file() is wrapped against OSError so a name that's
invalid for the platform degrades instead of raising.

Transitive sources (a→b→c) remain unresolved, as the issue specifies.

Testing

Three new tests in tests/test_extract.py — the two the issue asks for, plus a guard that
the bare-name branch still fabricates nothing:

$ uv run pytest tests/test_extract.py -q -k "extensionless_sourced_lib or bare_source_name_resolves or bare_source_missing_file"
3 passed, 149 deselected, 1 warning in 2.82s

Confirmed they catch the bugs — same tests with graphify/extract.py and
graphify/extractors/bash.py reverted to v8:

FAILED tests/test_extract.py::test_extract_bash_call_into_extensionless_sourced_lib_resolves - AssertionError: []
FAILED tests/test_extract.py::test_extract_bash_bare_source_name_resolves_to_sibling - AssertionError: []
2 failed, 150 deselected

Affected suites and both pre-commit gates:

$ uv run pytest tests/test_extract.py tests/test_symbol_resolution.py tests/test_languages.py -q
4 failed, 521 passed, 1 warning in 24.15s

$ uv run ruff check --config pyproject.toml graphify/extractors/bash.py graphify/extract.py tests/test_extract.py
All checks passed!

$ uv run python -m tools.skillgen --check
check OK: 134 artifact(s) match committed output and expected/.

Those 4 failures are pre-existing on Windows, not from this PR — they're exactly the 4
test_extract.py failures in my baseline on unmodified v8 (66d8110), all symlink-related
(test_collect_files_*, e.g. OSError: [WinError 1314] A required privilege is not held by the client). Full-suite baseline there is 45 failed / 3578 passed / 15 skipped. No
Linux/macOS box here to confirm they're green, so please read that in context.

[safishamsi]

Thanks @Souptik96. Shipped in v0.9.27 (cherry-picked to v8), with a follow-up marking the bare-name binding INFERRED (it resolves via $PATH at runtime). Closed-unmerged here, but it's in the release: https://github.com/Graphify-Labs/graphify/releases/tag/v0.9.27