Platform: Dashboard page — remove local components, use unified MetricCard and Badge, add Breadcrumbs

[8dazo]

Summary

Clean up the dashboard page by removing local MetricCard/SpendCard/StatusBadge definitions and replacing with unified components from #97 and #98.

Current Defect

• Local MetricCard in dashboard/page.tsx is a more complex version of components/metric-card.tsx — two conflicting implementations
• Local SpendCard has 3 color variants (slate/cyan/emerald) but isn't a shared component
• Local StatusBadge uses rounded-full border — inconsistent with Badge component's rounded-md no-border
• Cards use hardcoded colors (border-slate-800, bg-slate-950/80) instead of semantic tokens
• No breadcrumbs

Solution

• Remove local MetricCard, SpendCard, and StatusBadge from dashboard/page.tsx
• Use unified MetricCard (Platform: Unify MetricCard — replace two implementations with single component #97) for all 4 metric cards and 3 spend cards
• Use Badge status variant (Platform: Add Badge status variants + custom components (CopyButton, CodeBlock, FileUpload) #98) for COMPLETED/FAILED/BLOCKED statuses
• Migrate SpendCard logic into MetricCard variant or extract as SpendCard component
• All Cards use semantic tokens: border-border, bg-card, text-card-foreground
• Add Breadcrumb: Projects > [Project Name] > Dashboard

Files to Modify

• Modify: apps/platform/app/projects/[projectId]/dashboard/page.tsx

Acceptance Criteria

• No local MetricCard/SpendCard/StatusBadge definitions in dashboard/page.tsx
• All metrics use unified MetricCard with appropriate variants
• Status badges use Badge status variant
• All colors use semantic tokens (no hardcoded slate/cyan)
• Breadcrumb shows navigation trail

Depends on #95, #96, #97, #98
Part of #dashboard-ui-modernization