refactor: Message Components for Accessibility and Responsiveness

1. Description
   Several UI components in packages/fuselage/src/components/Message/ lack accessibility features such as appropriate ARIA attributes, roles, keyboard navigation support, or focus management. Additionally, some components are not fully responsive and may not adapt gracefully to different device sizes or themes. This impacts both usability and inclusiveness of Rocket.Chat's UI.

2. Proposed Solution

• Audit all Message components for accessibility and responsiveness gaps.
• Add ARIA roles and attributes (e.g., role="region", aria-label, etc.) to support screen readers.
• Ensure all interactive elements are reachable and usable via keyboard navigation, implementing logical focus order and focus trapping where necessary.
• Refactor layouts using modern CSS techniques (Flexbox, Grid, clamp()) for responsive design across mobile, tablet, and desktop screens.
• Replace hardcoded styles with theme variables or CSS custom properties to support dynamic theming and maintain strong color contrast.
• Update color, font size, padding, etc. to meet WCAG 2.1 guidelines.
• Add or enhance tests: unit tests, a11y checks with jest-axe, and potentially E2E for critical flows.

3. Why this matters

• Ensures Rocket.Chat is inclusive and usable for all users, including those relying on assistive technologies.
• Makes the product more robust and ready for enterprise or public sector adoption, where accessibility is a requirement.
• Enhances the experience for all users across varied devices and display settings.
• Aligns Rocket.Chat's UI framework with industry standards and best practices, supporting GSoC-level contributions.

Start by auditing the components in packages/fuselage/src/components/Message/ for the accessibility and responsiveness gaps described in the issue. Define the affected components and checks first; done means the agreed ARIA, keyboard, focus, responsive, theming, WCAG, and jest-axe coverage is implemented, with E2E coverage where critical flows require it.