[Studio][Bug] ACL user and rule search do not escape SQL LIKE wildcards

## Problem

ACL inventory search treats `%` and `_` as SQL LIKE wildcards instead of literal characters:

- `GET /api/acl/users/page?keyword=` filters `username` and `access_key` with unescaped `LIKE`.
- `GET /api/acl/rules/page?principal=` / `?resource=` filter `principal` and `resource` the same way.

Usernames and ACL principals commonly contain underscores (`svc_monitor`, `prod_user`). Searching for `prod_user` therefore also matches `prodXuser`, and a trailing `%` matches any suffix — so the inventory silently returns unrelated accounts or rules.

## Evidence

`MybatisPlusAclRepository.findUserPage` (`server/src/main/java/org/apache/rocketmq/studio/instance/acl/MybatisPlusAclRepository.java:115-129`) lowercases the keyword and passes it straight into `.like(username, search).or().like(access_key, search)`.

`MybatisPlusAclRepository.ruleQuery` (`:388-398`) does the same for `principal` and `resource`.

The same class of defect was already fixed for query history (`QueryHistoryService.escapeLike`) and is being fixed for instance / audit / cloud-credential / Studio-user search; ACL inventory is the remaining high-traffic search surface with the gap.

## Impact

Operators cannot reliably look up the ACL account or rule they mean when the identifier contains `_` or `%`. In a shared Studio with many service accounts this produces wrong rows (including other accounts' access keys in the page listing) and can hide the intended rule.

## Expected behavior

User-supplied `keyword`, `principal`, and `resource` are matched literally. Escape `\`, `%`, and `_` before building the LIKE pattern (same convention as `QueryHistoryService.escapeLike`). Blank/null filters keep their current no-filter semantics.

## Acceptance criteria

- Regression tests prove a keyword such as `prod_user%` is bound as `%prod\_user\%%` rather than `%prod_user%`.
- Cover both the user page search and the rule page principal/resource search.
- Do not change the public API contract.

## Related work

#2265 / `QueryHistoryService.escapeLike` established the escape convention. Open peers: #4223 (Studio user search), instance / audit / cloud-credential LIKE PRs.

Start in server/src/main/java/org/apache/rocketmq/studio/instance/acl/MybatisPlusAclRepository.java, reviewing findUserPage and ruleQuery, then compare their LIKE handling with QueryHistoryService.escapeLike. Add regression coverage for user keyword and rule principal/resource searches, and verify that backslashes, percent signs, and underscores are bound literally while blank filters retain their current behavior.

Written by the indexing model from the issue text.