feat: Add gRPC Support

[TBA5854]

Description
We want to introduce gRPC-based communication for the Server-Driven UI (SDUI) system to replace or complement the existing REST/JSON approach.

The goal is to:

• Improve performance (binary serialization, HTTP/2)
• Enable strongly-typed UI contracts
• Support bi-directional streaming for real-time or progressive UI updates
• Make SDUI more scalable and maintainable across clients
• With gRPC, the server will send UI schemas / component trees defined via .proto messages, and the client will render the UI dynamically based on these definitions.

Requirements:

• Define protobuf schemas for SDUI components (layout, widgets, actions, styles)
• gRPC service for fetching UI definitions
  Example: GetScreen(ScreenRequest) -> ScreenResponse
• Support versioning of UI schemas to avoid client breakage
• Enable bi-directional or server streaming for:
  • Incremental UI loading
  • Live UI updates (experiments, feature flags, real-time state)
• Ensure backward compatibility with existing REST-based SDUI (if applicable)
• Client-side gRPC support (mobile/web) with graceful fallback
• Proper error handling and empty/partial UI responses
• Authentication & authorization support (metadata / interceptors)
• Documentation for proto definitions and rendering rules

Additional Context

gRPC is preferred due to:

• Lower payload size vs JSON
• Contract-first development
• Better multi-platform client generation
• This enables A/B testing, feature flags, and remote UI experiments without app updates
  Especially useful for:
  • Home screens
  • Dashboards
  • Dynamic forms
  • Experiment-heavy flows

Optional future extension:

• Cacheable UI responses
• UI diff / patch streaming instead of full screen reloads