chore: refactor Docker workflows and remove GoReleaser configuration

[creativeprojects]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.76%. Comparing base (65f4135) to head (8f4ed3e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #666   +/-   ##
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  Coverage   81.76%   81.76%           
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  Files         161      161           
  Lines       12009    12009           
=======================================
  Hits         9818     9818           
  Misses       1692     1692           
  Partials      499      499           

Flag	Coverage Δ
unittests	80.01% <ø> (ø)

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[Copilot]

Pull request overview

This PR refactors how Docker images are built and published by moving multi-arch build logic out of GoReleaser and into a reusable composite GitHub Action, while updating the Makefile and Dockerfile to support cross-compiled binaries for container builds.

Changes:

• Introduces a composite action (.github/actions/docker-build) to build/push multi-arch images (amd64/arm64) and deduplicates workflow logic.
• Updates the Makefile to add build-ci for cross-compiling container binaries and renames prep/mock targets.
• Removes GoReleaser Docker-only configuration and related pre-hooks, switching Docker publishing to dedicated workflow jobs.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
Makefile	Renames prep/mock targets and adds build-ci for Docker image cross-compilation.
CONTRIBUTING.md	Updates docs to match renamed Makefile targets.
build/Dockerfile	Switches to copying arch-specific resticprofile binaries from build/.
.goreleaser.yml	Removes Docker-related hooks/config and manifests from GoReleaser.
.goreleaser-docker-only.yml	Deletes the Docker-only GoReleaser config.
.github/workflows/snapshot.yml	Switches nightly image build to the new composite action.
.github/workflows/release.yml	Separates Docker image publishing into its own job using the composite action.
.github/workflows/docker.yml	Refactors scheduled/manual rebuild workflow to use the composite action.
.github/actions/docker-build/action.yml	Adds composite action encapsulating buildx setup, binary downloads, cross-compile, and build/push.

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