[v0.9] Expose theme from ComponentContext

[jacobsimionato]

Currently, ComponentContext has access to the SurfaceModel, which contains the surface's theme configuration. However, to improve ergonomics for renderer and component developers, we should expose the theme property directly on the ComponentContext.

This is a prerequisite for wiring up consistent theme support across all A2UI renderers.

This is a child issue of #734.

[jacobsimionato]

Coding agent prompt: Expose the theme object from SurfaceModel directly on ComponentContext for easier access by component implementations.

Implementation Strategy

1. Modify @renderers/web_core/src/v0_9/rendering/component-context.ts.
2. Add a get theme() property to the ComponentContext class that returns this.surface.theme.
3. Ensure the return type correctly reflects the theme structure defined in @renderers/web_core/src/v0_9/state/surface-model.ts (typically any or a Record until more strictly typed).
4. Update unit tests in @renderers/web_core/src/v0_9/rendering/component-context.test.ts to verify that the theme provided during surface creation is accessible via the context.

Context

• @renderers/web_core/src/v0_9/rendering/component-context.ts
• @renderers/web_core/src/v0_9/state/surface-model.ts
• @renderers/web_core/src/v0_9/rendering/component-context.test.ts

[jacobsimionato]

@ava-cassiopeia @ditman I think we should do this ASAP, and in the theming, make sure our standard catalog is making use of the "primary color" property on the basic catalog theme.