Frontend toast/notification system for error feedback

[ryuhmanov-m]

Parent issue: #20

Context

When backend operations fail (reindex, git operations, config save), users see no feedback. Errors are logged to console but not surfaced in the UI.

Scope

Build a reusable toast/notification component:

1. Create src/components/ui/Toast.tsx — a notification component with:
   • Variants: success, error, warning, info
   • Auto-dismiss (configurable timeout, default 5s)
   • Manual dismiss button
   • Stack multiple toasts
2. Create a toast store or context (useToast hook)
3. Add <ToastContainer /> to the root layout
4. Wire up 2-3 existing error paths as proof of concept (e.g., reindex failure, settings save error)

Design

Follow the existing design system (shadcn/ui + Tailwind). Keep it minimal — no external toast libraries.

References

• Existing UI components: src/components/ui/
• Global layout: src/app/layout.tsx