[Bug] SHOW TIMESERIES WHERE TAGS(...) CONTAINS is Case-Sensitive While Timeseries CONTAINS is Case-Insensitive

### Search before asking

- [x] I searched in the [issues](https://github.com/apache/iotdb/issues) and found nothing similar.

### Version

apache iotdb = 2.0.5

### Describe the bug and provide the minimal reproduce step

I'm encountering inconsistent behavior in SQL queries involving `CONTAINS` filters on timeseries metadata. When searching timeseries by `TAGS`, the `CONTAINS` operator behaves case-sensitively.

```sql
SHOW TIMESERIES WHERE TAGS(description) CONTAINS "Flow";
```
This returns results correctly because one of my timeseries has a tag `description="Flow"`.

But if I change the search to:
```sql
SHOW TIMESERIES WHERE TAGS(description) CONTAINS "flow";
```
It returns no results, even though `"Flow"` exists.
So tag-based `CONTAINS` filtering is case-sensitive.

### What did you expect to see?

`CONTAINS` should behave consistently across metadata fields, ideally being case-insensitive.
For **timeseries names**, the same query type is already **case-insensitive**:
```sql
SHOW TIMESERIES WHERE Timeseries CONTAINS "Flow";
```
This matches `"Flow"`, `"flow"`, `"FLOW"`, etc.

### What did you see instead?

#### Why This Matters:

* TAG searches are commonly used for metadata filtering and discovery.
* Case-sensitive matching makes searching inconsistent with other IoTDB metadata filters.
* It forces users to know exact casing of tags, reducing usability.

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Bắt đầu với các truy vấn SHOW TIMESERIES trong issue, so sánh TAGS(description) CONTAINS với Timeseries CONTAINS bằng cách sử dụng các kiểu viết hoa khác nhau. Truy vết phần triển khai của các bộ lọc siêu dữ liệu này và bổ sung coverage cho các ví dụ đã được báo cáo; được xem là hoàn tất khi TAGS CONTAINS hoạt động nhất quán với hành vi Timeseries CONTAINS hiện có, vốn không phân biệt chữ hoa chữ thường.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.