chore: add CI scaffold and CHANGELOG

[AhmedAredah]

Summary:

• Add a Linux GitHub Actions CI workflow with mandatory markdown lint checks, an advisory clang-format dry run, and a non-blocking build-linux scaffold.
• Add CHANGELOG.md using Keep a Changelog format with the initial 0.0.1 entry.
• Add the CI status badge to the README badge block.

Build dependency note:

• build-linux is continue-on-error and is intentionally non-blocking while dependency bootstrap hardens.
• Container is checked out through the private CONTAINER_REPO_TOKEN secret and pinned to the v0.2.0 release tag.
• KDReports is checked out from the latest release tag, kdreports-2.3.0; CI patches that release generated Qt6 package config before configuring CargoNetSim.
• Ubuntu librabbitmq-dev uses flat amqp*.h headers, so CI creates a compatibility include directory for the project rabbitmq-c/amqp.h includes.
• clang-format is advisory because the existing source tree has formatting drift and this PR does not touch source files.
• Win/macOS CI are deferred to a follow-up.

Test plan:

• Actions tab shows the workflow ran on this PR.
• lint job passes; markdownlint is blocking, and clang-format reports current source formatting drift without blocking this scaffold.
• build-linux is allowed to fail; expected failures should be readable and point to dependency bootstrap or build issues.
• README badge renders and links to the CI workflow.