feat: make main drive tags, releases, and docker publish

[jigarkhwar]

What changed

• moved the release flow into ci so main now computes the next version, creates the git tag, runs GoReleaser, and publishes Docker Hub tags
• kept PR image validation, and added a dedicated main image build that uploads the validated Docker image as an artifact
• publish now loads and pushes the validated image artifact instead of rebuilding it in a separate workflow
• removed the old tag-only release.yml, the separate docker-publish.yml, and the no-longer-needed docker release metadata action
• added a reusable release-version action to calculate the next tag from conventional commits

Flow

• pull_request: test -> integration -> local Docker build and docker run version
• push to main: test -> integration -> compute version -> build/validate Docker image -> create git tag -> GoReleaser release notes/assets -> push Docker Hub tags

Docker tags

• without the v prefix
• .
• latest

Checks

• go test ./...
• go test -tags=integration -race -count=1 ./...
• local version calculation currently resolves from v0.9.0 to v0.9.1