feat: implement emoji icon picker for goals

[HarikaPokalakari]

Summary

Implemented emoji icon picker feature
allowing users to add, change and remove
icons on their savings goals.

Changes Made

src/api/types.ts

• Added icon field to Goal interface:
  icon: string | null

src/api/lib.ts

• Added updateGoal PUT request function
• Connects frontend to backend for
  persistent icon storage

src/ui/pages/Main/goals/GoalCard.tsx

• Added Icon styled component
• Displays emoji icon on each goal card

src/ui/features/goalmanager/GoalManager.tsx

• Added icon and emojiPickerIsOpen state
• Added addIconOnClick function
• Added pickEmojiOnClick function
• Added deleteIconOnClick function
• Added EmojiPicker component
• Added GoalIcon component
• Icons persist after page refresh ✅

New Files

• src/ui/components/EmojiPicker.tsx
  Reusable emoji picker using emoji-mart
• src/ui/features/goalmanager/GoalIcon.tsx
  Displays goal icon with click handler

How to Test

1. npm run start
2. Click any goal card
3. Click smile icon → emoji picker appears
4. Pick any emoji → shows on goal card ✅
5. Refresh page → emoji still showing ✅
6. Click icon → change emoji ✅
7. Click Remove icon → icon deleted ✅