fix: replace invalid diff tool with bash in security-reviewer agents (#89)

`diff` is not a valid Claude Code tool name — the agent would silently
lose its diff capability at runtime. Use `bash` to invoke diff instead.

Applies to all four locales: en (07-plugins), vi, zh, uk.

Co-authored-by: Claude Code <noreply@anthropic.com>

zh/07-plugins/pr-review/agents/security-reviewer.md

@@ -1,7 +1,7 @@
 ---
 name: security-reviewer
 description: 面向安全的代码审查
-tools: read, grep, diff
+tools: read, grep, bash
 ---
 
 # 安全审查员