github: add Claude code review workflow triggered by /claude comment

github: add Claude code review workflow triggered by /claude comment

Add claude-code-review.yml using anthropics/claude-code-action@v1.
The review runs when a PR comment containing "/claude" is posted,
avoiding unnecessary API usage on every push.

Uses issue_comment trigger restricted to PR comments only. Only
triggers for users with write access (OWNER, MEMBER, COLLABORATOR)
and when the comment body contains "/claude", preventing any runner
from being allocated for unrelated comments. A short domain hint
steers the review toward OpenWrt embedded Linux conventions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Link: https://github.com/openwrt/openwrt/pull/22556
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>