Make AI Investigations docs platform-agnostic

[qsellem]

What does this PR do? What is the motivation?

The AI Investigations pages added in #36350 were unintentionally browser-flavored (mentions of JavaScript, page loads, browser profiling, third-party scripts, etc.). Single-View AI Investigation actually runs on any RUM view — Browser, iOS, Android, Flutter, React Native — with no platform gating in the frontend or the backend stream API.

This PR rewords the affected sentences and table rows to be platform-agnostic:

• "page load" → "page or screen"; "the browser" → "the application"; "JavaScript bundle" → "heavy client-side computation"; "long tasks blocking the main thread" → "main-thread blocking"; etc.
• "Browser profiling" → "RUM profiling correlation" (the linked correlation page already covers Browser, iOS, and Android).
• App Performance and Third Party row descriptions reworded to drop browser-specific terminology.

No factual claims about coverage are added — only existing browser-leaning phrasings are made generic.

Merge instructions

Merge readiness:

• Ready for merge

Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/quentin.sellem/rum_single_view_investigation_fix/real_user_monitoring/ai_investigations/
• https://docs-staging.datadoghq.com/quentin.sellem/rum_single_view_investigation_fix/real_user_monitoring/ai_investigations/single_view_ai_investigation