ci: Switch PR review workflow to Opus 4.7 via Mantle endpoint

Opus 4.7 is in research preview on Bedrock and the Invoke API rejects
the beta headers Claude Code sends ("invalid beta flag"). Enable the
Mantle endpoint, which serves Claude via the native Anthropic API shape
and accepts those headers, and switch the model ID to the Mantle form
(no region prefix or version suffix).

.github/workflows/claude-review.yml

@@ -192,6 +192,7 @@ jobs:
         env:
           CLAUDE_CODE_DISABLE_BACKGROUND_TASKS: "1"
           CLAUDE_CODE_USE_BEDROCK: "1"
+          CLAUDE_CODE_USE_MANTLE: "1"
         run: |
           mkdir -p ~/.claude
 
@@ -369,7 +370,7 @@ jobs:
           PROMPT
 
           claude \
-            --model us.anthropic.claude-opus-4-6-v1 \
+            --model anthropic.claude-opus-4-7 \
             --effort max \
             --max-turns 200 \
             --setting-sources user \