Fix CI: install protobuf-compiler for proto compilation

The build requires protoc to compile the gRPC proto definitions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: script3r

.github/workflows/ci.yml

@@ -13,6 +13,8 @@ jobs:
         uses: actions/checkout@v4
       - name: Install Rust
         uses: dtolnay/rust-toolchain@stable
+      - name: Install protoc
+        run: sudo apt-get update && sudo apt-get install -y protobuf-compiler
       - name: Build
         run: cargo build
       - name: Test