refactor(dialog): improve composition model and accessibility

[ruben-rebelo]

Refactor Dialog to improve Material Design 3 compliance, remove problematic children patterns, improve performance characteristics, and modernize the public API.

Problems

• Current API relies heavily on children composition in ways that are difficult to optimize
• Internal layout logic is tightly coupled to arbitrary child structures
• MD3 behaviors and visuals are not fully aligned with current Material guidelines
• Rendering performance can degrade in large lists or frequently updated screens
• Type safety and discoverability of the API can be improved
• The component has inconsistent behavior between platforms and edge cases

Focus Areas

• Simplify Dialog.Title / Dialog.Content / Dialog.Actions hierarchy
• Improve keyboard and accessibility handling
• Improve MD3 spacing and tonal elevation
• Reduce excessive wrappers

Proposed API Direction

<Dialog title="Delete item" content="Are you sure?" actions={[...]} />

Performance Opportunities

• Reduce nested layout complexity
• Improve portal interaction handling
• Reduce unnecessary rerenders during visibility updates

[adrcotfas]

Important

See #4949 for more details