Polish dashboard UI and add audited, forkable examples

[mohsinht]

The dashboard needs stronger visual hierarchy, readable charts on narrow screens, and complete examples that forkers can adapt safely.

This PR adds contrasting metric tiles, geometry-preserving chart reveals, contained chart scrolling, visible data disclosures, and touch/keyboard donut selection. It removes misleading positional hover effects and uses neutral change text when a number's sign does not determine its meaning.

Three complete synthetic dashboards live under /examples: daily cockpit, money overview, and work focus. The examples have deliberate block spans, coherent next actions, source warnings, and reconciled cash-runway calculations. npm run examples ignores local identity and private snapshots. The existing schema and owned shadcn-compatible primitives remain in place.

The design system documents composition, tokens, motion, accessibility, and fork adaptation. The UI audit records findings and limits. Twelve full-page local Chromium screenshots cover all examples on desktop/mobile in light/dark.

Validation:

• Full npm run check passed: 53 tests, contracts/privacy, build, coverage, tutorial, performance, accessibility.
• Normal dashboard and showcase audited at 320, 390, 768, 1024, and 1440px in both themes.
• Chart disclosure/toggle, keyboard Space, reduced motion, document overflow, dialogs, navigation, and built-in palettes checked.
• 111 KB JS, 10 KB CSS, 87 KB normal demo data, gzip, within budgets.
• Remote tree exactly matches the staged local tree.

Screenshots and reproduction: examples/README.md
Audit: docs/ui-audit-showcase.md

Scope is zaati-os only. No private repository, scheduled task, or deployment changes. Browser emulation and automated checks do not replace physical-device or human screen-reader testing.