#23485 ci: run the feat-cmux-next familiar-intent warning from main

This adds intent-familiar-review.yml to main. It's the advisory warning on feat-cmux-next PRs that edit a stability=familiar intent without an Intent-Delta: line. GitHub takes a pull_request_target workflow from the default branch whatever the PR's base. The copy that exists only on feat-cmux-next (#20544, #20726) was never registered, so it has never run.

This is the same move as #23428. The file is the feat copy plus a header note. The checker, scripts/ci/intent_familiar_warning.py, is still checked out at the PR's base commit, so feat-cmux-next's version runs, never main's. The trigger stays limited to branches: [feat-cmux-next]. The job is advisory: it never fails a check.

Proof after merge: a ready probe PR on feat-cmux-next that touches an @intent ... stability=familiar line should get the cmux-familiar-intent-warning comment. I'll close the probe with a comment.

Changelog

• None (CI only).

No capture: workflow-only change.

Agent session: cosmic-gray

🤖 Generated with Claude Code

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Summary by cubic

Registers the familiar-intent warning workflow on main, where GitHub sources pull_request_target workflows from, so it finally runs on feat-cmux-next PRs.

• The trigger stays limited to branches: [feat-cmux-next].
• The checker script is still read from the PR's base commit, so the feat-cmux-next version of the logic runs.
• The job is advisory only and never fails a check; it posts or updates a cmux-familiar-intent-warning comment when a PR edits a stability=familiar intent without an Intent-Delta: line.

Summary by CodeRabbit

• New Features
  • Added automated pull-request checks that review changes for familiar-intent concerns.
  • Posts or updates advisory comments with affected files and review guidance.
  • Runs automatically during pull-request lifecycle events.