Clarify directory and filename wildcards in extraction mappings

[xuu33030]

Summary

Closes #286 by clarifying the existing extraction-pattern semantics, without changing matching behavior.

** includes one or more filename characters, while **/ can match zero directory levels without consuming the filename prefix. Therefore **._*.py does not match ._module.py or pkg/._module.py; **/._*.py does.

• Document the distinction, with the working ignore rule placed before the Python extraction rule.
• Correct the description of *: it matches one or more characters, not an empty string.
• Keep the pathmatch() docstring consistent and add parametrized coverage of the documented behavior.

The current semantics date back to the original pathmatch implementation; this deliberately avoids a potentially incompatible change to extraction mappings.

Verification

On CPython 3.13.5:

• python -m pytest -q tests/test_util.py babel/util.py tests/messages/test_extract.py tests/messages/test_extract_python.py tests/messages/test_js_extract.py tests/messages/test_jslexer.py — 95 passed.
• ruff check babel/util.py tests/test_util.py (0.14.10) — passed.
• git diff --check — passed.
• An additional temporary-directory check executed extract_from_dir() on root-level and nested ._module.py files plus a normal pkg/module.py: the reported pattern extracted all four files, while the documented replacement extracted only the normal file. These are behavioral documentation tests, not a claim of a production-code red/green fix.

Sphinx 9.1.0 strict HTML builds were run against both this branch and an unmodified archive of base commit 6ba6701. Both reported the same five existing diagnostics: extract_javascript docstring indentation and unresolved targets in dates.rst, dev.rst (two), and the unrelated entry-point section of messages.rst. The documentation build is not reported as passing. No full CLDR-dependent suite or multi-platform test matrix was run locally.

AI disclosure

This contribution was prepared and verified with Hermes Agent. No independent human review is claimed.