[Bug] Incorrect capacity check in Server#LocalStorage

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)

### Search before asking

- [X] I have searched in the [issues](https://github.com/apache/incubator-uniffle/issues?q=is%3Aissue) and found no similar issues.

### Describe the bug

When uniffle shuffle-servers colocate with other services (like Hadoop HDFS data), they shares the same mounted disks.

If so, the current capacity checking is wrong, it only will check the uniffle's data used size instead of using the free disk size.

### Affects Version(s)

master

### Uniffle Server Log Output

_No response_

### Uniffle Engine Log Output

_No response_

### Uniffle Server Configurations

_No response_

### Uniffle Engine Configurations

_No response_

### Additional context

_No response_

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

Start at Server#LocalStorage and trace how its capacity check measures disk usage. Reproduce the colocated-service scenario described in the issue, then verify that the check accounts for free space on the shared mounted disk rather than only Uniffle's data usage; add or update a relevant regression test if the project provides one.

Written by the indexing model from the issue text.