feat: Comprehensive employee management system improvements

- ✨ Added compact employee forms (add/edit) with all fields visible
- 🎯 Implemented expandable employee rows with timesheet integration
- 📊 Added real KPI calculation based on work hours, sick days, and overtime
- 📅 Added bulk date selection and editing in calendar
- 🗓️ Implemented day-specific editing modal with hours and overtime tracking
- 💾 Extended database schema with overtimeHours field
- 🎨 Improved UI layout: tabs left, search right, real current date display
- 🧹 Fixed spacing issues and removed unnecessary gaps
- 🔧 Enhanced GraphQL mutations for employee schedule management

prisma/schema.prisma

@@ -331,15 +331,16 @@ model Employee {
 }
 
 model EmployeeSchedule {
-  id          String         @id @default(cuid())
-  date        DateTime
-  status      ScheduleStatus
-  hoursWorked Float?
-  notes       String?
-  employeeId  String
-  createdAt   DateTime       @default(now())
-  updatedAt   DateTime       @updatedAt
-  employee    Employee       @relation(fields: [employeeId], references: [id], onDelete: Cascade)
+  id            String         @id @default(cuid())
+  date          DateTime
+  status        ScheduleStatus
+  hoursWorked   Float?
+  overtimeHours Float?
+  notes         String?
+  employeeId    String
+  createdAt     DateTime       @default(now())
+  updatedAt     DateTime       @updatedAt
+  employee      Employee       @relation(fields: [employeeId], references: [id], onDelete: Cascade)
 
   @@unique([employeeId, date])
   @@map("employee_schedules")