feat: Toast Notification System (Bounty #825)

[liuyuzhe530]

Bounty: Toast Notification System (Bounty #825)

Reward: 150,000 $FNDRY | Tier: T1 | Domain: Frontend

What was built

A complete toast notification system matching all acceptance criteria:

• 4 variants: success (emerald), error (red), warning (amber), info (cyan)
• Auto-dismiss after configurable duration (default 5s) with visual countdown progress bar
• Slide-in animation from top-right corner
• Toast stacking — up to 5 toasts displayed simultaneously, oldest removed first
• Accessible — role="alert", aria-live="polite", keyboard-dismissible
• Global API — showToast(variant, title, description, duration) and toast.success/error/warning/info() functions
• SolFoundry dark theme — forge-900 bg, forge border, brand color accents

Files changed

• frontend/src/components/ui/Toast.tsx — new toast component + provider
• frontend/src/main.tsx — wrapped app in ToastProvider

Usage

import { toast } from '@/components/ui/Toast';

toast.success('Bounty Claimed!', 'Your submission is under review.');
toast.error('Transaction Failed', 'Insufficient funds in your wallet.');
toast.warning('Deadline Approaching', '2 hours remaining to submit.');
toast.info('New Bounty Available', 'Check the bounty board for opportunities.');

Closes #825