docs.yml: skip PR comment step on fork PRs instead of suppressing 403

Fork PR runs always get a read-only GITHUB_TOKEN regardless of the
permissions: block. The previous approach attempted the comment and
relied on continue-on-error to swallow the 403, leaving a red step.

Replace the condition with a same-repo guard so the step is simply
skipped for fork PRs. The comment will still post for PRs opened within
the bemanproject/optional repo itself.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: steve-downey

.github/workflows/docs.yml

@@ -62,11 +62,11 @@ jobs:
       # where the docs-site artifact can be downloaded and inspected.
       # Uses a hidden marker so the comment is updated (not duplicated) on
       # each push to the PR branch.
-      # continue-on-error because fork PRs may lack write permission for
-      # pull-requests; the build still passes even if the comment fails.
+      # Skip on fork PRs: the GITHUB_TOKEN in a fork PR run is always
+      # read-only regardless of the permissions: block, so the comment
+      # would 403. Only attempt it when the PR is within the same repo.
       - name: Post or update PR preview comment
-        if: github.event_name == 'pull_request'
-        continue-on-error: true
+        if: github.event_name == 'pull_request' && github.event.pull_request.head.repo.full_name == github.repository
         uses: actions/github-script@v7
         with:
           script: |