feat: add consumption tracking for services

Enhanced services module with comprehensive consumption tracking:
- Add usage field to ServiceBill interface (optional number)
- Add unit field to ServiceBill interface (kW, m³, or empty for internet)
- Updated AddServiceModal with consumption input field
- Auto-detect unit based on service type (electricity=kW, gas/water=m³, internet=none)
- Responsive grid layout for amount and consumption inputs
- Display consumption and unit in history list
- Show price per unit in history (amount/usage)
- Improved date display with responsive layout

🤖 Generated with [Claude Code](https://claude.com/claude-code)

lib/types.ts

@@ -66,6 +66,8 @@ export interface ServiceBill {
   id: string
   type: 'electricity' | 'water' | 'gas' | 'internet'
   amount: number
+  usage?: number
+  unit?: string
   date: string
   period: string // YYYY-MM
   isPaid: boolean