refactor(dialog): improve composition model and accessibility

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**

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**Performance Opportunities**

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

Start by locating the Dialog component and reviewing its current children-based composition, portal behavior, and visibility updates. Compare the existing public API with the proposed title, content, and actions props, then assess the keyboard, accessibility, MD3 spacing, tonal elevation, and wrapper changes. Done means a coherent API and consistent behavior across the stated platforms and edge cases, with improved rendering characteristics.

Written by the indexing model from the issue text.