Improve Chapter 01 Linux distributions lesson

[jules-tth]

Scope

• Reworks the Chapter 01 Linux distributions lesson around operator decision-making instead of a generic distro overview.
• Adds distribution-family comparison, read-only evidence commands, package-manager checks, release/support notes, command-portability cautions, troubleshooting signals, hands-on practice, and review questions.

Verification

• python -m pip install -r requirements.txt could not run because python is not on PATH.
• python3 -m pip install -r requirements.txt passed.
• python3 -m mkdocs build --strict passed.
• make build passed.
• git diff --check passed.
• find docs -type f -name '*.md' -size 0 -print returned no files.\n- No dedicated repo-local link/check script was found beyond MkDocs/Makefile build paths.\n\n## Duplicate-prevention\n\n- Checked open PRs from jules-tth; PR Improve Chapter 01 orientation #3 covers the Chapter 01 README, PR Improve Chapter 01 sysadmin duties lesson #299 covers 1.01, PR Improve Chapter 01 suggested background lesson #300 covers 1.02, and no open PR touched docs/lessons/01_where_to_start/1.03_linux_distributions.md immediately before PR creation.

[jules-tth]

Reviewer assignment to bdorlus failed: GraphQL: jules-tth does not have the correct permissions to execute RequestReviewsByLogin (requestReviewsByLogin).