ci: publish Docker from release workflow

[VdustR]

Summary

• publish Docker Hub images from the Release Please workflow when a release is created
• keep the Docker workflow as a manual backfill/repair path for existing release tags
• update README and AGENTS release-flow notes to match the new behavior

Why

GitHub does not trigger a second workflow from events created by the default GITHUB_TOKEN, so a GitHub Release created by Release Please does not reliably fire a separate release: published Docker workflow. Publishing Docker in the same release workflow keeps the normal release path deterministic.

Verification

• ruby -e 'require "yaml"; ARGV.each { |path| YAML.load_file(path); puts path }' .github/workflows/*.yml
• git diff --check
• .venv/bin/python -m pytest -q
• .venv/bin/python -m compileall -q src/font_splitter tests
• .venv/bin/python -m build

Risks

• Docker publishing now shares the Release Please workflow. If Docker Hub publishing fails after a GitHub Release is created, the manual Docker workflow remains available for backfill.
• The Docker workflow no longer runs on release: published; this is intentional because that trigger was unreliable for releases created by GITHUB_TOKEN.

[changeset-bot]

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Latest commit: 117b6fa

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[gemini-code-assist]

Code Review

This pull request updates the documentation in AGENTS.md and README.md to reflect changes in the release and Docker publishing workflows. Specifically, it documents that Docker images are now published as part of the main release workflow to avoid reliance on secondary triggers, and updates version references from v0.2.0 to v0.2.1 in examples. I have no feedback to provide as there were no review comments.