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Fix outdated navigation guidance, improve readability.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Fix outdated navigation guidance, improve readability.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

[rcastley]

The following is a really valid statement that needs to be kept

The Spring PetClinic application uses a single HTML page as the "layout" page, that is reused across all pages of the application. This is the perfect location to insert the Splunk RUM Instrumentation Library as it will be loaded in all pages automatically.

[adamjsr]

My PR does keep this statement intact for the most part. Some of the content surrounding the statement does change though.