Migrate to the shared automation-template.yml entry point

Overview

This repo copies one caller workflow from learningequality/.github, call-pull-request-target.yml.
learningequality/.github#88 deletes the reusable workflow behind it, so that caller must be replaced
with the new shared template. The template also switches on ten automations this repo does not run
today, so please confirm that you want them before merging.

Complexity: Low
Target branch: release-v0.9.x

Context

call-pull-request-target.yml calls pull-request-target.yml in learningequality/.github, which
routes three automations: review-requested, pull-request-label and dependabot-reviewer.

learningequality/.github#88 flattens that dispatcher into a central reusable automation.yml and
deletes pull-request-target.yml. Once that merges, this repo's caller breaks, so the two changes
must land together.

The replacement is one template that every consumer copies. Its on: block is generated as the
union of every enabled automation, so it is the same file everywhere. There is no per-repo subset:
learningequality/.github#86 chose central control, with automations enabled or disabled for the
whole org in a registry.

The Change

Replace call-pull-request-target.yml with one copy of automation-template.yml from
learningequality/.github, saved as .github/workflows/automation.yml. Do not edit the copy.

This repo keeps the three automations it runs today and gains ten more:

Automation	Trigger
contributor-pr-reply	Pull request opened by a contributor
holiday-message	Pull request opened, issue comment created
issue-open	Issue opened or reopened
issue-label-header	Issue labeled or unlabeled help wanted
good-first-issue-comment	Issue labeled good first issue or help wanted
update-pr-spreadsheet	Pull request assigned, opened, closed, edited, and more
community-contribution-label	Issue assigned or unassigned
contributor-issue-comment	Issue comment created
resolve-bot-pr-threads	Pull request review comment created
unassign-inactive-issues	Weekly schedule and manual dispatch

Most of these act on community contribution flows. If this repo receives no community issues or
pull requests, they stay quiet.

Out of Scope

• Changing what any automation does.
• Editing the copied template to remove automations. The on: block is generated, and a local edit
  will drift from learningequality/.github.

Coordination

learningequality/.github#88 is the source of truth for this migration. Read it for the design, the
full consumer list, and the current state.

Do not merge this repo's pull request on its own. The order is fixed:

1. Every migration pull request, across all eight consumer repos, is approved and left unmerged.
2. learningequality/.github#88 merges first. From that point, any repo that has not merged yet loses
   review-requested, pull-request-label and dependabot-reviewer, because that pull request
   deletes the pull-request-target.yml that the old caller uses.
3. The eight migration pull requests merge in succession, straight after. Each merge restores its
   own repo.

Merging this repo's pull request first does not work either. The copied template calls
automation.yml@main, and that file does not exist until learningequality/.github#88 lands.

Acceptance Criteria

• .github/workflows/automation.yml is an unedited copy of automation-template.yml from
  learningequality/.github@main.
• call-pull-request-target.yml is deleted.
• This pull request is merged only after learningequality/.github#88.
• LE_BOT_APP_ID and LE_BOT_PRIVATE_KEY resolve in a workflow run in this repo.
• The four optional secrets are confirmed present or accepted as absent. They are
  SLACK_WEBHOOK_URL, SLACK_COMMUNITY_NOTIFICATIONS_WEBHOOK_URL,
  CONTRIBUTIONS_SPREADSHEET_ID, CONTRIBUTIONS_SHEET_NAME and
  GH_UPLOADER_GCP_SA_CREDENTIALS. An absent secret does not disable its automation. The
  automation runs and its step fails.
• After merge, requesting a review, labeling a pull request, and opening a dependabot pull
  request each behave as they did before.

Testing

1. Request a review on a test pull request. Confirm that the reviewer routing still runs.
2. Add a label to a test pull request. Confirm that the label handling still runs.
3. Open a test issue and label it help wanted. Confirm that the header is added.
4. Check the Actions tab after the first weekly run. Confirm that unassign-inactive-issues
   either succeeds or fails only on the Slack step.

References

• learningequality/.github#88 is the source of truth for this migration.
• learningequality/.github#86 is the original tracking issue. It stays open until all eight
  migrations land.
• docs/automation.md in learningequality/.github describes the entry point and the secrets.

AI usage

I used Claude Code to inspect the caller workflows in this repo and to draft this issue. I verified
the automation list and the secret names against learningequality/.github myself, and I edited the
wording.