Add Sorting Option for Budget Proposals by Latest Comment

## Description
Introduce a new sorting option to **sort budget proposals by the latest comment**.
This will allow users to easily find the most recently discussed proposals and follow ongoing conversations.

## Acceptance Criteria
- [ ] A **"Latest Comment"** option is added to the sorting dropdown for budget proposals.
- [ ] Selecting this option sorts proposals based on the **timestamp of the most recent comment**.
- [ ] Sorting applies across all views where budget proposals are listed.