Improve course overview learning path

[jules-tth]

Scope

• Expands docs/course/overview.md with the course operator loop, chapter workflow, safety boundaries, and capstone evidence expectations.
• Adds links to lab setup, syllabus, glossary, and capstone from the overview page.

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.

Duplicate check

• Checked open PRs from jules-tth; no open PR touches docs/course/overview.md.

[jules-tth]

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