docs(user): fix broken links in observability page

[mesutoezdil]

Fixes broken links in docs/user/observability.md. They pointed to old paths; the real pages live under docs/user/metrics/.

Tested: verified each link target exists, ran ./tools/ci/check-docs (0 errors).

Refs: NO-REF

[coderabbitai]

📝 Walkthrough

Walkthrough

Updated observability documentation links to reference new locations for metrics, gRPC proxy metrics, dashboards, and State Metrics Service metrics.

Changes

Observability documentation

Layer / File(s)	Summary
Update observability documentation links docs/user/observability.md	Updated links in the question table and application-level statistics section to the new observability documentation paths.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: fixing broken links in the observability documentation page.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{Comment @coderabbitai help to get the list of available commands.}

[pdmack]

This PR is one of four that together fix the lychee link check failures currently blocking CI on other PRs (e.g. #252). Verified locally: with #240, #241, #242, and #261 all applied, lychee --offline and fern check both pass with zero errors.

Note: broader broken-link issues remain visible via fern check --broken-links (14 additional errors in nav-tree resolution, pre-existing and out of scope here).

@sbaum1994 -- can you review and approve so these can merge?