chore(ci): add issue triage, stale, and Slack PR automation

[anfibiacreativa]

What this does

This adds a set of GitHub Actions bots and issue/PR templates to help us keep
the backlog tidy without much manual effort. There is no runtime or site-visible
change here, it is all repo automation under .github/.

Included:

• Issue forms (bug and feature) with required fields that drive triage: an
  "Experience Workspace (EW)" question, a Scope / Area picker, customer-vs-developer,
  and priority (P0 to P3). Blank issues are disabled.
• triage-assign: applies the ew label when EW is selected, adds a scope:*
  label, and auto-assigns the area owner(s) based on scope.
• issue-completeness: on open or edit, checks the issue has what triage needs
  (description, customer-vs-developer, priority, and for bugs the repro steps and a
  repro link). If something is missing it applies triage-incomplete and leaves a
  single comment that tags the reporter and clears once the issue is complete. A
  video is prompted but never blocks.
• pr-ew-review: when a PR ticks the "Experience Workspace (EW)" box, it applies
  the ew label and requests review from the core team (excluding the PR author).
• slack-pr-ticker: posts a note to Slack when a PR is opened, routing core vs
  external contributions to separate channels.
• stale: warns then closes inactive issues (60 days, then 21) and PRs (49 days,
  then 14). Any activity resets it, and pinned / security / keep-open /
  milestoned items are exempt.
• CONTRIBUTING.md documents all of the above.

Notes before this is fully live

• The event-driven workflows and the issue forms only take effect once this is on
  main, so nothing runs from the branch alone (stale can be triggered manually via
  workflow_dispatch to smoke-test).
• The Slack ticker needs two secrets, SLACK_WEBHOOK_CORE_PRS and
  SLACK_WEBHOOK_COMMUNITY_PRS. It fails safe and just skips if they are absent.
• One scope area is named "Heli" as a placeholder, happy to rename it if there is a
  better label.

Fix #

Test URLs:

• Not applicable, this PR only changes .github/ automation.

Experience Workspace (EW)

• This PR touches Experience Workspace (EW)

[aem-code-sync]

Hello, I'm the AEM Code Sync Bot and I will run some actions to deploy your branch.
In case there are problems, just click the checkbox below to rerun the respective action.

• Re-sync branch

Commits

• 0872a62 ✅ (latest)
• b8e0b86 ✅
• 45532e7 ✅
• 0f01a90 ✅
• a898ba2 ✅
• afa7d59 ✅
• f556556 ✅
• 9a465bf ✅

[anfibiacreativa]

Thanks @maximilianvoss @mhaack , this is much tighter now. Here's what changed based on the review:

• Dropped the "Is this EW related?" question from the issue forms and the PR
  template, and removed the pr-ew-review workflow and ew labeling with it (@mhaack).
• Removed the Helix option from the Scope list (@mhaack).
• Triage now just applies a scope label, no auto-assignment. We work from the
  prioritized board instead, which is what you were after (@maximilianvoss).
• Swapped "Customer request or developer need?" for "Who is affected?"
  (customer-facing or internal). It keeps the signal we use to triage impact
  without the feature-request framing.
• Removed the Priority field entirely, since we set priority on the board.
• Reworked the stale flow so nothing closes out of nowhere: a soft check-in first
  with no close pressure, then a final notice about a week before close, then
  close. It only applies to items created since March 1 so it does not sweep the
  old backlog, and a hold or awaiting-maintainer label pauses it for PTO or
  when the wait is on us (@mhaack).

I kept the Scope list as is (MCP and friends included) and the structured
reproduction link field, since one intake door and queryable fields are what let
us build the board later.