cli/docs/tests: harden config edit invocation and add YAML empty-export coverage

[oib]

Motivation

• Improve the robustness of the CLI editor invocation for aitbc config edit to avoid fragile os.system usage and handle complex EDITOR values.
• Ensure config export returns an empty mapping for an empty .aitbc.yaml when exporting in both JSON and YAML formats.
• Fix inconsistent documentation links and conservative Python-version notes in the docs.

Description

• Replaced os.system(...) with a tokenized invocation using shlex.split(...) + subprocess.run(...) and ensured EDITOR is stripped with a nano fallback in cli/aitbc_cli/commands/config.py.
• Made YAML export resilient to empty files by using yaml.safe_load(f) or {} so exports of empty .aitbc.yaml yield an empty mapping.
• Updated tests in tests/cli/test_config.py to patch the new subprocess.run target and added test_export_empty_yaml_yaml_format to assert YAML-format export of an empty config returns {}; also kept existing JSON empty-export test.
• Updated docs: unified the GitHub Discussions/Issue Tracker links and adjusted Python version references in docs/8_development/1_overview.md and docs/1_project/3_infrastructure.md for consistency.

Testing

• Ran PYTHONPATH=cli pytest -q tests/cli/test_config.py which completed successfully with 32 passed.
• Ran a local link-existence scan against docs/8_development/1_overview.md which reported no missing local links.

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