[Task]: Refactor task page details UI

[luizhcastro]

Objective

Refactor the task details page UI to integrate all new features (history, relationships, comments, milestones) into a modern, cohesive interface that improves user experience and task management workflow.

Figma design: https://www.figma.com/design/fwgpxrsQ9mFoA30JR3c7xu/Blaboard---Prototype?node-id=196-1190&t=WROYgVHwUEmU8HrQ-4

Scope

Frontend Implementation:

• Implement new page layout structure
• Build timeline/activity feed component
• Implement comments UI with threading and reply functionality
• Add @mention autocomplete in comment box
• Integrate all backend APIs ([Task]: Implement milestones #54, [Task]: Implement relationships/dependencies between tasks #55, [Task]: Implement history and logs on task #56, [Task]: Implement chat discussions and threads for tasks with @ mentions #57)
• Add markdown preview and rendering
• Implement responsive layout for mobile

Testing & Quality:

• E2E tests for main user flows
• Cross-browser testing
• Mobile responsiveness testing
• Code review completed

Acceptance criteria

• New page layout is visually consistent with design system
• Timeline/activity feed displays all task events
• Dependencies section clearly shows blocked/blocking relationships
• Comments support threading and @mentions work correctly
• All backend features are integrated and working
• Responsive layout works on mobile and tablet
• Loading states provide clear feedback
• E2E tests cover critical user flows
• Code review approved by team