Add browser SDK setup options to Cdocs browser partial

[rtrieu]

What does this PR do? What is the motivation?

Updates the Cdocs browser SDK setup partial to restructure the setup section into three distinct options:

• Option 1: Manual client-side setup — existing content, reorganized under a numbered heading
• Option 2: Server-side auto-instrumentation — adds inline setup content with platform cards (Java, NGINX, Windows IIS, Apache, IBM HTTP) and a GovCloud unavailability notice
• Option 3: Agentic Onboarding — extracted into a new reusable partial (layouts/shortcodes/mdoc/en/agentic-onboarding/setup.mdoc.md) for AI-assisted SDK instrumentation via Cursor or Claude Code

Also adds a new browser-auto-instrumentation-limitations.mdoc.md partial.

Merge instructions

Merge readiness:

• Ready for merge

Additional notes

[rtrieu]

Closing — change was accidentally committed to the wrong branch. New PR incoming.

[github-actions]

⚠️ Possible site support note detected

The following files have a site-region shortcode at the top of the page that mentions a feature being "not available" or "not supported":

• content/en/session_replay/heatmaps.md

Are you trying to document site support for a product? If so, the site-region shortcode is not the recommended approach. See the Documenting site support guide for the preferred method.

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/rtrieu/add-browser-setup-options/session_replay/heatmaps