chore: remove orphan docs/metrics-reference.md

[TerrifiedBug]

Summary

Follow-up to #177. The docs/metrics-reference.md file lived at the docs root rather than under docs/public/, so the previous cleanup pass missed it.

The page has been ported to the standalone docs site at https://vectorflow.sh/docs/reference/metrics (added in commit TerrifiedBug/vectorflow.sh@main on the vectorflow.sh repo) and added to the Reference sidebar.

Test plan

• find docs -name "metrics*" returns no results
• https://vectorflow.sh/docs/reference/metrics renders the same content
• Reference sidebar on vectorflow.sh shows "Metrics" as the last entry

[greptile-apps]

Greptile Summary

This PR deletes the orphaned docs/metrics-reference.md file that was missed in the previous cleanup pass (#177) because it lived at the docs root rather than under docs/public/. The content has already been published to the standalone docs site at vectorflow.sh/docs/reference/metrics, so no information is lost.

Confidence Score: 5/5

Safe to merge — pure documentation file deletion with no code changes.

No code, logic, or security changes. The deleted file is a standalone Markdown doc whose content has already been published externally. No findings of any severity.

No files require special attention.

Important Files Changed

Filename	Overview
docs/metrics-reference.md	Deleted orphan documentation file (349 lines); content has been ported to vectorflow.sh/docs/reference/metrics per PR #177 follow-up.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["docs/metrics-reference.md<br/>(deleted)"] -->|"content ported to"| B["vectorflow.sh/docs/reference/metrics"]
    B --> C["Reference sidebar entry: Metrics"]

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_{Reviews (1): Last reviewed commit: "chore: remove docs/metrics-reference.md ..." | Re-trigger Greptile}