refine tooltip placement and affordance

[AugistineCreates]

This pr closes #100

Implemented a fully accessible, responsive tooltip component that replaces the previous simple hover‑click behavior.

• Added keyboard activation (Enter/Space) and Escape key handling, with focus return to the trigger after closing.
• Implemented touch support: taps toggle the tooltip without generating duplicate mouse events.
• Added automatic edge‑collision detection and placement flipping between top and bottom based on available space.
• Updated the trigger button to a larger hit area (8 × 8 px) with a clear focus ring and a larger info icon.
• Refactored tooltip styling into reusable base and placement class strings for consistent theming.
• Added an arrow that points correctly according to the placement (top or bottom).
• Ensured ARIA compliance with role="tooltip" and dynamic aria-describedby.

All changes are limited to src/app/components/ui/tooltip.tsx. The component is now used in the wallet card and other UI elements without further modifications. No new dependencies were added.

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