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

Adds a Closed PR workflow that fires a posthog-ci-pr-stats event when a PR is
merged, mirroring the measurement already running in PostHog/posthog. Events go
to project 2 via POSTHOG_API_TOKEN and carry repository/actor metadata (added by
posthog-github-action v1.2.0) so PR velocity can be tracked per repo.

Generated-By: PostHog Code
Task-Id: 50da29c4-f95f-45b8-83a5-f0682414bedf

Author: pauldambra

.github/workflows/pr-closed.yml

@@ -0,0 +1,49 @@
+name: Closed PR
+
+on:
+    pull_request:
+        types:
+            - closed
+
+permissions:
+    contents: read
+    pull-requests: read
+
+jobs:
+    report-pr-age:
+        name: Report age of PR
+        runs-on: ubuntu-24.04
+        timeout-minutes: 5
+        if: github.event.pull_request.head.repo.full_name == github.repository && github.event.pull_request.merged == true
+        steps:
+            - name: Calculate PR age
+              env:
+                  PR_CREATED_AT: ${{ github.event.pull_request.created_at }}
+                  PR_HREF: ${{ github.event.pull_request._links.commits.href }}
+                  PR_TITLE: ${{ github.event.pull_request.title }}
+              run: |
+                  pr_age=$((($(date '+%s') - $(date -d "$PR_CREATED_AT" '+%s'))))
+                  echo "pr_age=$pr_age" >> $GITHUB_ENV
+
+                  first_commit_message_in_pr=$(curl -s "$PR_HREF" | jq '.[0].commit.message')
+                  echo "first_commit_message_in_pr<<EOF" >> $GITHUB_ENV
+                  echo "$first_commit_message_in_pr" >> $GITHUB_ENV
+                  echo "EOF" >> $GITHUB_ENV
+
+                  if [[ $first_commit_message_in_pr =~ Revert[[:space:]] ]]; then
+                      echo "is_revert=true" >> $GITHUB_ENV
+                  else
+                      echo "is_revert=false" >> $GITHUB_ENV
+                  fi
+
+                  # Escape the PR title for JSON
+                  pr_title_escaped=$(echo "$PR_TITLE" | jq -R .)
+                  echo "pr_title_escaped<<EOF" >> $GITHUB_ENV
+                  echo "$pr_title_escaped" >> $GITHUB_ENV
+                  echo "EOF" >> $GITHUB_ENV
+            - name: Capture PR age to PostHog
+              uses: PostHog/posthog-github-action@58dea254b598fb5d469c0699c98af8288a7f7650 # v1.2.0
+              with:
+                  posthog-token: ${{ secrets.POSTHOG_API_TOKEN }}
+                  event: 'posthog-ci-pr-stats'
+                  properties: '{"prAgeInSeconds": ${{ env.pr_age }}, "isRevert": ${{ env.is_revert }}, "prTitle": ${{ env.pr_title_escaped }}, "prNumber": "${{ github.event.pull_request.number }}"}'