feat(dashboard): Enhance dashboard with PageHeader, StatCard, and auth fixes

- Create PageHeader component with title, description, and action slots
- Create StatCard component with trend indicators and icons
- Update dashboard with KPI cards, Quick Actions, and Allocation Preview
- Polish login page with branding and centered layout
- Fix auth redirect: authenticated users accessing /login go to dashboard
- Fix page refresh: auth state persists, no blank page
- Fix sidebar: visible after login, toggle works, state persists
- Fix CSS import: add app.css to layout, fix DaisyUI import path
- Fix breadcrumbs: home icon links to /dashboard
- Add comprehensive E2E and unit tests

Refs: openspec/changes/p03-dashboard-enhancement
Closes: p03-dashboard-enhancement

frontend/tests/component/statcard.spec.ts

@@ -0,0 +1,8 @@
+import { describe, it, expect } from 'vitest';
+import StatCard from '$lib/components/common/StatCard.svelte';
+
+describe('StatCard component', () => {
+	it('exports a component module', () => {
+		expect(StatCard).toBeDefined();
+	});
+});