fix(frontend): resolve issues #879, #877, #875, #873

[girly-coder01]

Summary

This PR addresses 4 frontend issues with comprehensive fixes for testing, design tokens, component consolidation, and metadata:

Issue #879: Create tests for lib/amount.ts

• Added comprehensive test suite covering all functions in src/lib/amount.ts
• Tests validate formatAmount/parseAmount round-trip correctness
• Includes regression tests for stream creation wizard validation
• Covers hasValidPrecision, formatRate, truncateAmount, and formatCompactAmount

Issue #877: Replace hardcoded colors with CSS variables

• Replaced all hardcoded danger hex colors (#b12f3f, #8f2a38, #8c2230) with var(--danger)
• Updated affected classes: .activity-item span.is-negative, .dashboard-error-state h3, .secondary-button--danger, .wallet-error, .wallet-dropdown__warning
• Ensures consistency with design token system

Issue #875: Consolidate TransactionTracker components

• Removed redundant components/ui/TransactionTracker.tsx
• Migrated StreamCreationWizard to use inline step display
• Kept main components/TransactionTracker.tsx for incoming/page and ActivityHistory
• Eliminates duplicate component APIs and inconsistent visuals

Issue #873: Add metadata for social sharing

• Added metadataBase for absolute URL resolution
• Configured OpenGraph metadata (title, description, url, siteName, images)
• Added Twitter card configuration for summary_large_image
• Set canonical URL via alternates

Changes

• ✅ Created frontend/src/__tests__/lib.amount.test.ts with 150+ lines of tests
• ✅ Updated frontend/src/app/globals.css to use CSS variables
• ✅ Updated frontend/src/app/layout.tsx with complete metadata
• ✅ Updated frontend/src/components/stream-creation/StreamCreationWizard.tsx with inline step display
• ✅ Deleted redundant frontend/src/components/ui/TransactionTracker.tsx

Test Plan

• Run npm run test in frontend directory to verify all tests pass
• Verify lint checks pass with npm run lint
• Verify build succeeds with npm run build
• Check dashboard for proper color rendering with CSS variables
• Test stream creation wizard flow and confirmation steps
• Verify Open Graph tags are present in page head (check with social share preview tools)

Closes #879
Closes #877
Closes #875
Closes #873