chore(ci): capture PR age metrics to PostHog on merge

[pauldambra]

Problem

We track PR throughput and age-to-merge for PostHog/posthog via a posthog-ci-pr-stats event (the posthog-pr-metrics action in project 2), but PostHog/code has no equivalent, so its PRs are invisible in that view.

Changes

Adds .github/workflows/pr-closed.yml with a single report-pr-age job that, when a PR is merged from a branch in this repo, fires a posthog-ci-pr-stats event to PostHog project 2 (via the org POSTHOG_API_TOKEN secret — already used by this repo's pr-approval-agent.yml).

It mirrors the job already running in PostHog/posthog. Each event carries prAgeInSeconds, isRevert, prTitle, prNumber, plus repository/actor/actor_type metadata added automatically by posthog-github-action@v1.2.0 — so events from all repos land in the same project and can be split by repository.

CI-only; no runtime code changes. Forks are excluded (same-repo head check).

How did you test this?

Not yet runtime-tested — the capture only fires on a real merge event. I verified the workflow is valid YAML and that POSTHOG_API_TOKEN is already referenced by this repo's existing pr-approval-agent.yml, confirming the secret is available here. First merged PR after this lands will produce a posthog-ci-pr-stats event with repository=PostHog/code.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[pauldambra]

🤖 PostHog Code (automated agent) — posted on behalf of @pauldambra.

Closing in favour of an org-level approach: a single GitHub organization webhook feeding a PostHog incoming-webhook HogFunction that emits posthog-ci-pr-stats. That covers every repo (including future ones) with no per-repo workflow file, so this per-repo PR is no longer needed.