ci: Improve GitHub Actions workflows

[sirantd]

Summary

• Add concurrency groups to cancel redundant builds on new commits (e.g. rapid dependabot merges)
• Add PR build validation with hadolint linting and Dockerfile build check (no push)
• Remove duplicate GHCR build — copy manifest from DockerHub instead, halving build time
• Remove unnecessary QEMU setup (native ARM runners already used)
• Add GHA cache scoping to prevent matrix jobs from overwriting each other's cache
• Fix release workflow_dispatch condition that always skipped manual triggers
• Add missing PR title types: refactor, test, perf, build, revert
• Add authenticated GitHub API calls in version-check to avoid rate limiting
• Add AWS CLI and Helm S3 to version-check coverage

Test plan

• Verify PR triggers lint + validate jobs (no push)
• Verify push to main triggers full build + merge + copy-to-ghcr
• Verify workflow_dispatch on release workflow works
• Verify version-check runs without API rate limit errors

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[github-actions]

This PR is included in version 1.9.0 🎉