setup: include build-essential in default packages

[wyli]

Summary

• Add build-essential to the default holoscan setup package list so CUDA-base images (which ship ninja-build but no compiler) leave behind a working gcc/g++/make.
• No-op on bases that already ship gcc (SDK images, Ubuntu desktop), since install_packages_if_missing skips already-present packages.

Why

Holohub Jenkins build #484 (cuda12base-2404 stage, base = nvcr.io/nvidia/cuda:12.9.1-base-ubuntu24.04) failed in the post-setup cmake configure step:

```
CMake Error at applications/myproj/CMakeLists.txt:18 (project):
No CMAKE_C_COMPILER could be found.
No CMAKE_CXX_COMPILER could be found.
```

The default `holoscan setup` already provisions `cmake`, `ninja-build`, `python3-dev`, cuDNN, TensorRT, etc. — adding a compiler is the missing piece for the contract "after `holoscan setup`, a downstream Holoscan project can be configured and built." This change makes that contract hold on bare CUDA bases.

Test plan

• Pre-commit (ruff, isort, black, codespell) passes on the diff
• Manually: run `holoscan setup` on a fresh `nvcr.io/nvidia/cuda:12.9.1-base-ubuntu24.04` container and confirm `gcc --version` works
• Holohub Jenkins `cuda12base-2404` stage goes green once this lands on `main` (the holohub Dockerfile installs holoscan-cli from `git+https://github.com/nvidia-holoscan/holoscan-cli.git@main\` for that stage)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Improved code clarity in the setup process with enhanced comments and reformatted configuration lists.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Configuration used: Organization UI

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Run ID: f1c144a8-784c-4893-bb05-9834928abb79

📥 Commits

Reviewing files that changed from the base of the PR and between 19f4689 and 1620593.

📒 Files selected for processing (1)

• src/holoscan_cli/commands/setup_cmd.py

---

Walkthrough

The holoscan setup command now includes explanatory comments documenting why build-essential and related development tools are required. The package list argument to install_packages_if_missing has been reformatted across multiple lines for improved readability without changing which packages are installed or the surrounding setup flow.

Changes

Setup Command Documentation Enhancement

Layer / File(s)	Summary
Package installation documentation and formatting src/holoscan_cli/commands/setup_cmd.py	Explanatory comments clarify why build-essential and related tools are required. The package list passed to install_packages_if_missing is reformatted across multiple lines with identical package entries for improved readability. No behavioral changes to package installation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding build-essential to the default packages installed by the setup command.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[wyli]

do you know what the criteria we used to decide whether a package should be included in this auto-installation command? I'm writing some tests and I couldn't remember how we came up with this list.. @tbirdso

[tbirdso]

My recollection is that this is a loose list of tools that we either directly rely on in HoloHub CLI or otherwise see commonly represented across Holoscan projects

• General environment management: wget, git, unzip
• holohub build tooling: cmake, ,ninja-build
• Tools commonly used at build or runtime in Holoscan projects: xvfb, ffmpeg, libv4l-dev

[tbirdso]

Thanks @wyli for investigating. My initial thoughts are:

• We intentionally do not declare a default language in HoloHub default CMake setup in order to avoid artificially requiring Python projects to have an unused C/C++ compiler in their environment
• I wonder if the test pipeline intentionally declares that the project is using the CXX language in CMake? If not, the error output seems like a possible bug:

CMake Error at applications/myproj/CMakeLists.txt:18 (project):
No CMAKE_C_COMPILER could be found.
No CMAKE_CXX_COMPILER could be found.

• Regardless, I am OK with adding build-essential to ./holohub setup with the reasoning that "this is a foundational package that we observe many common HoloHub subprojects rely on"