feat: Add GitHub Flow semantic anchor

[Copilot]

GitHub Flow is a widely-adopted Git workflow whose name alone activates a rich, consistent knowledge cluster in LLMs — making it a high-value semantic anchor for compact, precise prompting with coding agents.

Changes

• docs/anchors/github-flow.adoc — English anchor covering core concepts (always-deployable main, short-lived feature branches, PR-as-collaboration-unit), 6-step workflow, proponent (Scott Chacon, 2011), and when-to-use guidance
• docs/anchors/github-flow.de.adoc — German translation
• website/public/data/anchors.json — Entry inserted alphabetically between gherkin and gof-abstract-factory-pattern; categories: development-workflow; roles: software-developer, devops-engineer, team-lead; related: conventional-commits, semantic-versioning
• skill/semantic-anchor-translator/references/catalog.md — Entry added under "Development Workflow" so agents using the skill can discover and suggest this anchor

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Anchor Proposal]: GitHub Flow</issue_title>
<issue_description>### Proposed Term

GitHub Flow

Context (Optional)

GitHub Flow is one of the most widely adopted Git workflows in the software industry, making it a strong candidate for a semantic anchor. When used in LLM communication, a single mention of "GitHub Flow" immediately activates a rich, consistent knowledge cluster: issue-driven development, short-lived feature branches, Pull Request-based review, the principle that main is always deployable, and the connection to continuous delivery practices.

This makes prompts significantly shorter and more precise. Instead of explaining "create a branch from main, name it after the issue, open a PR for review, merge only after approval" — you simply say "follow GitHub Flow" and the agent understands the full contract.

This is especially valuable when working with coding agents and AI assistants, where context window efficiency matters and repeated workflow explanations add noise. GitHub Flow as a semantic anchor also serves as a natural bridge to related concepts like Conventional Commits, Issue-Driven Development, and trunk-based deployment — making it a useful reference point in a broader agentic dev workflow conversation.

Pre-submission Checklist

• I have searched existing anchors and this term is not already included
• This term refers to a well-established concept (not something I invented)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Anchor Proposal]: GitHub Flow #178

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