Show available targets when test/docs run without a target

`just test` / `just docs` with no argument now print their available
targets instead of erroring, improving discoverability of the
argument-dispatched recipes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: laughingman7743

justfile

@@ -18,9 +18,12 @@ lint:
     uv run mypy .
 
 # Run tests: just test (pyathena|sqla|sqla-async)
-test target:
+test target="help":
     @just _test-{{target}}
 
+_test-help:
+    @echo "Available test targets: pyathena, sqla, sqla-async"
+
 _test-pyathena: lint
     uv run pytest -n 8 --cov pyathena --cov-report html --cov-report term tests/pyathena/
 
@@ -35,9 +38,12 @@ tox:
     uvx tox@{{TOX_VERSION}} -c pyproject.toml run
 
 # Docs: just docs (build|lint|format)
-docs target:
+docs target="help":
     @just _docs-{{target}}
 
+_docs-help:
+    @echo "Available docs targets: build, lint, format"
+
 _docs-build:
     uv run sphinx-multiversion docs docs/_build/html
     echo '<meta http-equiv="refresh" content="0; url=./master/index.html">' > docs/_build/html/index.html