set up claude pr auto-review

adds auto-review and migrates the existing @claude mention workflow to
the org-wide reusable workflows in bluesky-social/.github, matching
tango. adds a social-app-specific review prompt covering platform
parity, ALF/Lingui conventions, React Compiler, and the design system.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.github/workflows/claude-mention.yml

@@ -0,0 +1,23 @@
+name: claude-mention
+
+# Thin caller for the org-wide reusable @-mention workflow in
+# bluesky-social/.github. Shares the same prompt as claude-review.yml.
+
+on:
+  issue_comment:
+    types: [created]
+
+# See the corresponding comment in claude-review.yml re: why these
+# explicit permissions are necessary for reusable workflows.
+permissions:
+  contents: read
+  pull-requests: write
+  issues: write
+  id-token: write
+
+jobs:
+  mention:
+    uses: bluesky-social/.github/.github/workflows/claude-mention.yml@v1
+    secrets: inherit
+    with:
+      prompt-file: .github/claude-review-prompt.md