Add Lapdog Uninstall section and sidebar nav entry

[Kyle-Verhoog]

What does this PR do? What is the motivation?

The Lapdog page shipped without a sidebar nav entry, so it was only reachable by search or direct link. It also had no on-page uninstall procedure, sending users to the GitHub README for teardown steps.

This PR:

• Adds an Uninstall section to `content/en/llm_observability/lapdog.md` so the procedure (stop the agent, remove the Claude Code plugin and pi extension, delete `~/.lapdog`, then uninstall the package) lives on the docs page. The static dashboard's "Collecting sessions" popover deep-links to the new `#uninstall` anchor.
• Adds a Lapdog entry to the LLM Observability sidebar in `config/_default/menus/main.en.yaml`, placed between Instrumentation and Monitoring. The following top-level entries (Monitoring, Evaluations, Experiments, MCP Server, Data Security and RBAC, Terms and Concepts, Guides) get their `weight` bumped by 1 to make room. Sub-entry weights are unchanged (they sort relative to their parent).

Merge instructions

Merge readiness:

• Ready for merge

Additional notes

Vale was not run locally (binary not installed in my dev environment). Will rely on CI's Vale check.

Claude session: `1e26db38-e2e5-41d5-b214-b4a8c11b8ddb`
Resume: `claude --resume 1e26db38-e2e5-41d5-b214-b4a8c11b8ddb`

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/kyle.verhoog/llmobs-lapdog-uninstall-section/llm_observability/lapdog

[joepeeples]

Content looks good, but the process should be a numbered procedure, not separate headings/sections for each step. Could you reformat the procedure? Thanks!