Rework container builds

[inetol]

enh: move to file based script
enh: custom podman
fix: arm64 images
feat: add docker.io registry
enh: cleanup

Closes #213

[Copilot]

Pull request overview

This PR reworks container image building and publishing to use a file-based mise task with custom Podman setup, while adding Docker Hub as an additional image registry for redundancy.

Changes:

• Replaces the container CD build/push flow with mise run build:container and static Podman setup.
• Updates the Dockerfile build/runtime stages for multi-architecture standalone binaries.
• Documents Docker Hub usage and adjusts ignore rules/configuration for the new mise task layout.

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
README.md	Documents multiple container registries and updates validation instructions.
Dockerfile	Reworks builder/runtime image construction and architecture targeting.
.oxfmtrc.json	Updates formatter options.
.mise/tasks/build/container.sh	Adds the container build/publish task.
.mise/snippets/get_ctx.sh	Adds Git commit context helper.
.mise/snippets/condition_cmd.sh	Adds command availability guard helper.
.mise/snippets/condition_ci.sh	Adds CI environment guard helper.
.gitignore	Allows .mise task files to be tracked.
.github/workflows/cd.yml	Replaces action-based container build/push with mise + Podman workflow steps.
.dockerignore	Includes .mise files in the Docker build context.

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