Update LP/guide creation skills + validation to be compliant-by-default

## Context

Follow-on from #457 and #578. Implements the "shift left" changes identified by the audit so learning-path/guide PRs are compliant-by-default at creation time. Also absorbs #433 (dogfood/review feedback from PR #424), which already identified three concrete gaps captured below.

## Scope

- Update the LP/guide creation skill(s) (`/create-learning-path`, `/build-interactive-lj`, and related references) to enforce or prompt for the authoring rules identified in #578, including the known gaps from #433:
- Framing in/out of `milestones` by role (same framing rules as review)
- False noop detection / authoring so create doesn't emit numbered learner-action noops
- Section bookends outside the section (rule 14)
- Adjust creation-phase validation (`/lint`, `/check`, `/attack`, skill phases) so "ready for PR" already means "mostly review-ready"

## Success criteria

- [ ] Creation skill(s) updated to prevent/catch the top recurring findings from #578
- [ ] Milestone framing, false-noop, and section-bookend gaps from #433 are fixed
- [ ] `/lint` / `/check` / `/attack` reflect the same bar

## Related

Part of epic #577. Depends on #578. Split from #457. Absorbs #433.