fix: use specific versions instead of @latest for Go tools

Issue:
- google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest fails
- Error: '"latest" is not a valid version'
- @latest syntax has issues with some Go modules

Fix:
- Use specific versions:
  - protoc-gen-go@v1.36.1 (stable)
  - protoc-gen-go-grpc@v1.5.1 (stable)
- Check if already installed before attempting install
- Graceful fallback with warnings if installation fails

Behavior:
- If tool exists: [SKIP] already available
- If install succeeds: Silent success
- If install fails: [WARNING] but continues
- Never blocks the setup process

Result:
- Reliable installation with known-good versions
- No @latest version resolution issues
- Script continues even if Go tools fail