Add human resources statistics page with employee and leave breakdowns

Adds a new HR statistics page to the application, including routes, sidebar navigation, and data fetching for employee and leave statistics.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 3e5af67c-4a5a-48e3-8a89-01c833db26df
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Event-Id: f3b2aef9-6ea9-4936-af71-49e8398d3495
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/049d58e7-377a-4ecc-b278-702241ff7226/3e5af67c-4a5a-48e3-8a89-01c833db26df/psvpP4s
