feat: add WCAG compliant components (Toast, Modal, Tooltip, Tabs, Dropdown)

- Added robust, zero-dependency Toast notification system
- Added HTML5 dialog based Modal component
- Added React Portal based Tooltip component
- Added fully accessible Tabs component
- Added React Portal based Dropdown component with smart viewport edge collision
- Implemented strict WCAG keyboard navigation and ARIA roles across all new components
- Added a Components page to showcase all new UI components

Author: Asif Ansari

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "css.lint.unknownAtRules": "ignore"
+}