Apply PR review follow-ups for CI permissions, CPack metadata, and build docs

[Copilot]

This updates the branch with the concrete follow-ups requested in PR review: tighten workflow permissions for artifact publishing, correct CPack metadata handling, and align docs with the enforced Protobuf version constraint. Changes are intentionally minimal and scoped to the review comments.

• CMake packaging metadata

  • Bumped minimum CMake version to 3.9 to match use of project(... DESCRIPTION ...).
  • Fixed CPack summary assignment to preserve spaces in PROJECT_DESCRIPTION (quoted expansion).

• GitHub Actions workflow

  • Added actions: write at job permissions level so actions/upload-artifact can publish package artifacts while keeping contents: read.

• Build documentation

  • Updated docs/BUILD.md to explicitly call out Protobuf 3.21 exact for protobuf-compiler and libprotobuf-dev, matching find_package(Protobuf 3.21 EXACT ...).

cmake_minimum_required(VERSION 3.9 FATAL_ERROR)

set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "${PROJECT_DESCRIPTION}")

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

Pull request overview

This PR completes the repository “finish” layer by aligning CI, packaging, and contributor docs around a single CMake build/test/package workflow, and by adding basic project/package metadata for releases.

Changes:

• Hardened the Ubuntu GitHub Actions workflow (scoped triggers, least-privilege permissions) and added CPack packaging + artifact upload.
• Added CMake project() metadata (version/description) and enabled CPack TGZ generation.
• Updated README and added docs/BUILD.md to document the CI-aligned local build/test/package commands.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
docs/BUILD.md	Adds local prerequisites + CI-aligned build/test/package instructions.
README.md	Updates workflow badge and provides quickstart build/test/package commands.
CMakeLists.txt	Adds project metadata and CPack configuration for TGZ packaging.
.github/workflows/ubuntu.yml	Tightens CI triggers/permissions; uses canonical CMake steps; runs CPack and uploads TGZ artifacts.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

PROJECT_DESCRIPTION contains spaces, and unquoted expansion in set(CPACK_PACKAGE_DESCRIPTION_SUMMARY ${PROJECT_DESCRIPTION}) will turn it into a CMake list (semicolon-separated words), which can show up incorrectly in package metadata. Quote the value when assigning to the CPack variable.

Suggested change

	set(CPACK_PACKAGE_DESCRIPTION_SUMMARY ${PROJECT_DESCRIPTION})
	set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "${PROJECT_DESCRIPTION}")

[Copilot]

The build requires a specific Protobuf version (find_package(Protobuf 3.21 EXACT ...) in the root CMake). The prerequisites list only names packages, which can lead to confusing failures on distros that ship a different Protobuf version. Consider documenting the required Protobuf version (or relaxing the CMake version constraint if any 3.21+ works).

Suggested change

	- `protobuf-compiler`
	- `libprotobuf-dev`
	- `protobuf-compiler` (Protobuf 3.21 **exactly**, to match `find_package(Protobuf 3.21 EXACT ...)`)
	- `libprotobuf-dev` (Protobuf 3.21 **exactly**)

[Copilot]

project(... DESCRIPTION ...) requires a newer CMake than 3.5. With cmake_minimum_required(VERSION 3.5), configuration can fail on systems that actually use 3.5–3.8. Either bump the minimum required CMake version to one that supports DESCRIPTION, or remove DESCRIPTION and set PROJECT_DESCRIPTION/CPack summary another way.