fix(init): sanitize default package name derived from directory name

[Socialpranker]

Summary

Closes #10974.

poetry init/poetry new (which shares the same code path) used the current directory's name verbatim as the default package name. Per the PyPA name normalization spec, a valid name may only contain ASCII letters, numbers, period, underscore and hyphen — so a directory like my project with spaces produced a pyproject.toml with an invalid name = "my project with spaces" instead of name = "my-project-with-spaces".

This adds a small InitCommand._sanitize_package_name helper that replaces any disallowed character (including whitespace) with a hyphen, then reuses packaging.utils.canonicalize_name (already a dependency, already used elsewhere in this file for normalizing dependency names) to collapse/lowercase the result the same way it normalizes any other valid package name.

This only changes the default value derived from the directory name; an explicit --name/interactive value is left as-is, same as before.

Test plan

• Added test_sanitize_package_name — parametrized unit test covering the reported case plus a few edge cases (repeated separators, mixed ./_, leading/trailing separators).
• Added test_noninteractive_sanitizes_default_name_from_directory — reproduces the exact scenario from the issue (poetry init run non-interactively in a directory named my project with spaces), asserts the generated pyproject.toml has a valid name.
• pytest tests/console/commands/test_init.py - 73 passed
• pytest tests/console/commands/test_new.py - 24 passed (unaffected, NewCommand shares this code path)
• ruff check / ruff format --check - clean
• mypy src/poetry/console/commands/init.py - no issues

AI disclosure

This PR was written with the help of Claude Code (Claude Sonnet 5). All code was reviewed and tested by me before submission.

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• Consider handling the edge case where the sanitized name becomes empty after replacing invalid characters and stripping hyphens, as this could happen for directory names containing only disallowed characters.
• The _sanitize_package_name docstring currently describes the allowed character set for names but the canonicalization step produces only lowercase letters, numbers, and hyphens; clarifying that distinction would make the helper’s behavior easier to understand at a glance.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider handling the edge case where the sanitized name becomes empty after replacing invalid characters and stripping hyphens, as this could happen for directory names containing only disallowed characters.
- The `_sanitize_package_name` docstring currently describes the allowed character set for names but the canonicalization step produces only lowercase letters, numbers, and hyphens; clarifying that distinction would make the helper’s behavior easier to understand at a glance.

## Individual Comments

### Comment 1
<location path="src/poetry/console/commands/init.py" line_range="131" />
<code_context>
         name = self.option("name")
         if not name:
-            name = project_path.name.lower()
+            name = self._sanitize_package_name(project_path.name)

             if is_interactive:
</code_context>
<issue_to_address>
**issue:** Consider handling the case where sanitization produces an empty package name.

If `_sanitize_package_name` returns an empty string (e.g., when the directory name consists only of stripped characters), subsequent logic will operate on an invalid/empty project name. Please add a fallback for this case, such as raising an error or defaulting to a safe default name.
</issue_to_address>

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[sourcery-ai]

issue: Consider handling the case where sanitization produces an empty package name.

If _sanitize_package_name returns an empty string (e.g., when the directory name consists only of stripped characters), subsequent logic will operate on an invalid/empty project name. Please add a fallback for this case, such as raising an error or defaulting to a safe default name.

[Socialpranker]

The macOS aarch64 (Python 3.11) / mypy check failed, but it looks like a CI infrastructure issue rather than a real failure — the job was cancelled after 17m26s with "The job was not acquired by Runner of type hosted even after multiple attempts", and the same mypy check passes on every other Python version/platform combination. Could someone with the right access re-run that job?