Normalize course syllabus chapter labels

[jules-tth]

Scope

• Normalizes the course syllabus chapter labels to use consistent Chapter NN: Title formatting.
• Removes stale marketing-style subtitles and emoji from syllabus links while preserving existing links and lesson counts.
• Keeps this isolated to docs/course/syllabus.md so it does not conflict with the open chapter lesson PRs.

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.
• Final open-PR overlap check returned no open PR touching docs/course/syllabus.md.

[jules-tth]

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