gRPC Support

> ℹ️ _This issue was partially AI-generated and may contain technical inaccuracies._

**Is your feature request related to a problem? Please describe.**
gRPC services cannot be called from Trufos, which is increasingly requested in microservice-heavy environments.

**Describe the solution you'd like**
Support gRPC requests by loading `.proto` files, selecting services/methods, editing the message payload, and viewing responses (unary at minimum; streaming later).

**Describe alternatives you've considered**
Using grpcurl or a dedicated gRPC client.

**Additional context**
Niche but growing. Requires proto parsing and an HTTP/2 transport.

No files, tests, or entry points are named. Start by mapping the existing REST request flow, then scope proto loading, service and method selection, editable message payloads, response display, unary calls, and the required HTTP/2 transport; streaming can remain future work.

Written by the indexing model from the issue text.