Update 4-rum.md

[adamjsr]

Fix outdated navigation guidance, improve readability.

Summary

Fix outdated navigation guidance, improve readability.

Fixes # (optional — link an issue / ticket)

Type of change

• New workshop
• New chapter or page in an existing workshop
• [X ] Content edits (clarity, correctness, polish) to existing pages
• Restructure / reorganize (move, split, merge, renumber)
• URL change — aliases: added for any renamed or moved page
• Image / screenshot refresh
• Translation sync (content/en ↔ content/ja)
• Content removal / archival
• Theme bump or shortcode / layout adoption
• Frontmatter-only changes (weight, draft, hidden, archetype, …)
• Lint / formatting cleanup (low-risk, scan-approve)
• CI / build / tooling
• Bug fix (broken link, busted shortcode, etc.)
• Other — describe:

What's affected

• Workshop(s) / area: ninja-workshops/foundations/1-automatic-discovery/1-petclinic-monolith
• Languages: [ X] content/en    [ ] content/ja

Reviewer focus

N/A

Screenshots / preview

N/A

Verification

• hugo builds cleanly (no warnings or errors)
• npx markdownlint-cli2 '<paths/*.md>' passes for touched files
• Any new images have meaningful alt text
• No TODO image placeholders left unintentionally
• No published URLs changed, OR aliases: frontmatter added for any renamed / moved pages
• Identified and updated parallel / sibling pages where this workshop shares content with another (e.g. observability-cloud-short ↔ observability-cloud), OR confirmed none exist