v15.55.0

## What's Changed
* Adds translation to "Save" button in **Leave Application** form so the label appears in the user’s language. (https://github.com/frappe/hrms/pull/3926)
* Adds "Partially Billed" status to **Timesheet** to show when only part of the recorded work has been invoiced. **Salary Slip** now includes these timesheets when calculating payable hours. (https://github.com/frappe/hrms/pull/3950)
* Adds _Leave Encashment Amount Per Day_ to **Salary Structure Assignment**, letting payroll set a personalised rate for each employee. Leave encashment now uses this employee-specific rate and falls back to the salary structure’s default when the field is empty. (https://github.com/frappe/hrms/pull/3948)


**Full Changelog**: https://github.com/frappe/hrms/compare/v15.54.3...v15.55.0
**Authors**: @elshafei-developer, @nareshkannasln, @l0gesh29
**Reviewers**: @asmitahase

<details>
<summary>AI content</summary>

 For these release notes, we used an LLM (OpenAI o3) to review and summarise the code changes, along with the associated issue and PR descriptions. It may contain typical errors and inaccuracies. You can read the prompt [here](https://github.com/barredterra/pretty_release_notes). 

Changes with the following labels were excluded:
- skip-release-notes

Changes with the following types were excluded:
- test
 - style
 - refactor
 - ci
 - build
 - chore
 - docs

</details>