Add missing ARIA labels to icon-only buttons

[Mosas2000]

Description

This PR addresses issue #158 by adding missing ARIA labels to icon-only buttons throughout the application, ensuring WCAG 2.1 Level A compliance.

Changes Made

Components Updated

• ShareModal.tsx - Added aria-labels to social media share buttons (Twitter, Discord, Telegram, Reddit)
• MobileBottomSheet.tsx - Added aria-labels and aria-pressed states to snap point buttons
• DrawingToolsPanel.tsx - Added aria-labels to clear all, remove, undo, and redo buttons
• NotificationCenter.tsx - Added aria-labels to close and filter buttons with aria-pressed states
• CreateProposalModal.tsx - Added aria-label to close button
• PoolPositionRow.tsx - Added aria-labels to add and remove liquidity buttons

Documentation

• Created comprehensive ARIA label implementation guide
• Updated accessibility testing checklist
• Added integration examples and best practices
• Created accessibility improvements summary

Testing Infrastructure

• Added automated accessibility tests
• Implemented test coverage for ARIA labels
• Created reusable accessibility utilities and hooks
• Added accessibility-focused CSS utilities

Process Improvements

• Created accessibility-focused PR template
• Established guidelines for future accessibility work

WCAG Compliance

• Meets WCAG 2.1 Level A - 1.1.1 Non-text Content
• All icon-only buttons now have text alternatives
• Screen reader users can understand button purposes
• Keyboard navigation properly supported

Testing Performed

• Manual screen reader testing
• Automated accessibility audits
• Keyboard navigation verification
• Focus management validation

Impact

• Resolves accessibility violations
• Improves user experience for screen reader users
• Establishes foundation for ongoing accessibility compliance

Closes #158