fix: gate Forgejo review/comment triggers on @claude mention

Previously, all pull_request_comment events on Forgejo triggered the
full Claude pipeline unconditionally — both in the workflow if-condition
and in trigger.ts. This wasted CI resources and API credits on reviews
without @claude mentions (e.g. plain "LGTM" reviews).

Workflow: add @claude check via contains() on comment.body and review.body.
Trigger validation: replace blind auto-trigger with payload-aware check
that inspects available body fields, falling back only when no body exists.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.forgejo/workflows/claude.yml

@@ -26,7 +26,8 @@ jobs:
     #     despite action being 'labeled'). Let all through; trigger.ts validates.
     if: >-
       (github.event_name == 'issue_comment' && contains(github.event.comment.body, '@claude')) ||
-      (github.event_name == 'pull_request_review_comment' || github.event_name == 'pull_request_comment') ||
+      (github.event_name == 'pull_request_review_comment' || github.event_name == 'pull_request_comment') &&
+        (contains(github.event.comment.body, '@claude') || contains(github.event.review.body, '@claude')) ||
       (github.event_name == 'pull_request_review' && contains(github.event.review.body, '@claude')) ||
       (github.event_name == 'issues')
     runs-on: grunt