build: prevent gen_proto.sh from hanging (#736)

According to the [npx docs](https://docs.npmjs.com/cli/v8/commands/npx):

> If any requested packages are not present in the local project
dependencies, then they are installed to a folder in the npm cache,
which is added to the PATH environment variable in the executed process.
A prompt is printed (which can be suppressed by providing either --yes
or --no).

Running it in non-interactive manner hangs build process and waits for
keyboard input.

See #706 for potential long-term solution.

Was originally added in #696.

Author: ishymko

scripts/gen_proto.sh

@@ -2,7 +2,7 @@
 set -e
 
 # Run buf generate to regenerate protobuf code and OpenAPI spec
-npx @bufbuild/buf generate
+npx --yes @bufbuild/buf generate
 
 # The OpenAPI generator produces a file named like 'a2a.swagger.json' or similar.
 # We need it to be 'a2a.json' for the A2A SDK.