feat: Governance frontend panels + E2E test framework

[JoshLuedeman]

Summary

Adds 4 governance dashboard panels and sets up Playwright E2E testing framework.

Governance Frontend Panels

• CostPanel — Cost summary, budget utilization bar, top services breakdown
• RBACPanel — Health score, findings table with severity badges, scan trigger
• TaggingPanel — Compliance percentage, required tags, violations table
• AuditPanel — Audit entries table with action badges

GovernancePage Tabs

• TabList with 5 tabs: Overview, Cost Management, RBAC Health, Tagging, Audit Trail
• Conditional panel rendering based on selected tab

API Client Extensions

• 15 TypeScript interfaces for governance data types
• 4 new API subsections: \�pi.governance.cost, \�pi.governance.rbac, \�pi.governance.tagging, \�pi.governance.audit\

E2E Test Framework

• Playwright configuration with Chromium, auto-starts Vite dev server
• 3 smoke tests (homepage, navigation, 404)
• 4 governance dashboard tests
• 1 wizard flow test

Test Coverage

• 45 new component tests across 5 files (10 per panel + 5 page tests)
• All 1004 frontend unit tests passing

Closes #193