fix: validate problematic project paths

[skyswordw]

Adds project path validation in BaseCommand for known path characters that can break third-party build tools.

This validates the Briefcase project location separately from the existing data path validation:

• paths containing , raise an error
• paths containing U+200E LEFT-TO-RIGHT MARK raise an error on Windows
• paths containing spaces emit a warning banner

Fixes #2580

Validation performed:

• .venv/bin/python -m pytest -q tests/commands/base/test_paths.py -vv
• .venv/bin/python -m pytest -q tests/commands/base/test_paths.py tests/commands/base/test_validate_locale.py tests/commands/base/test_verify_tools.py tests/commands/base/test_properties.py
• .venv/bin/ruff format --check src/briefcase/commands/base.py tests/commands/base/test_paths.py
• .venv/bin/ruff check src/briefcase/commands/base.py tests/commands/base/test_paths.py

Not run: full pre-commit. Its first-time hook environment initialization hung locally after starting pre-commit-hooks, so I ran the relevant local pytest and ruff checks directly.

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by: OpenAI GPT-5.5