fix: Finalize metrics dashboard and resolve all outstanding issues

Created by: Edouard-Legoupil

This commit provides the final, stable version of the metrics dashboard. It resolves a 500 error in the backend API, removes unused code, and ensures all frontend visualizations are correctly implemented and displayed.

Backend changes (backend/api/metrics.py):

• Stabilized the /metrics/development-time endpoint by reverting it to its original, self-contained implementation.
• Corrected a query construction bug in the /metrics/cycle-time endpoint.
• Removed the unused /metrics/proposal-success-rate and /metrics/cycle-time endpoints to clean up the codebase.

Frontend changes (frontend/package.json):

• Added a dummy script to package.json to invalidate the build cache and force a re-generation of frontend assets.

Frontend changes (frontend/src/screens/Dashboard/components/MetricsDashboard/MetricsDashboard.jsx):

• Replaced all 'coming soon' placeholders with fully functional charts for 'Proposals by Category' and 'Donor Interest'.

• Confirmed that all new metrics are correctly visualized.

• Does my code meet the quality standards for releasing packages?

• Does the reviewer have all the information to validate the features/issues without too much research?

• Does the customer who will validate the associated tickets have the information to do so without wasting time?

Issues to validate to close :

• issue #

Processed issues to keep open or in progress:

• issue #

Checklist:

• Does the package check go local?
• Does the CI pass?
• Are the added / fixed features documented, tested?
• Are the added features / solved problems briefly presented in the PR message?
• Are the changes related to tickets / issues that I have listed in the commits and in the PR itself?
• Are the tickets in "review" mode in the Project Tracking Board?
• Does each ticket, if it is to be closed after acceptance of the PR, contain a comment that tells how to validate it?