[Studio][Feature] Compare ACL policies across instances

## Problem

Operators maintain equivalent ACL users and rules across production, staging, and disaster-recovery RocketMQ instances. Studio currently exposes one instance at a time, so policy reviews require manual exports and carry a risk of overlooking a missing or divergent grant.

## Proposed behavior

Add a read-only ACL comparison workflow that:

- loads complete paginated user and rule inventories from two instances;
- classifies policies as matching, drifted, source-only, or target-only;
- compares user administration, cluster association, read, and write permissions;
- compares rule actions, decision, and ACL version under a stable principal/resource identity;
- preserves duplicate logical rules instead of collapsing them;
- supports kind/status/search filters and filtered CSV export.

## Sensitive-data boundary

The comparison must never call credential reveal endpoints. Secret keys, masked secrets, access-key display variants, database ids, and creation timestamps are excluded from comparisons and exports.

## Acceptance criteria

1. Inventory walks are bounded and include every page.
2. Source and target can be swapped without stale results.
3. User and rule drift has field-level evidence.
4. CSV export follows active filters and contains no secret material.
5. Chinese and English UI text and focused regression tests are included.

## Scope

This feature is observational and does not create, update, delete, or synchronize ACL policies.

Start by locating the Studio ACL user and rule inventory entry points, the instance-switching state, and the CSV export flow. Trace how pagination, filters, and source/target changes are handled before checking existing focused tests. Done means read-only field-level drift comparison, filtered secret-free export, Chinese and English text, and regression coverage for the acceptance criteria.

Written by the indexing model from the issue text.