Document the GitHub account and repository model #1

Outcome

Publish one canonical explanation of the personal account, the .github and username-matching profile repositories, all source-repository responsibilities, community-file inheritance, planning, generated releases, CI, branch protection, licensing, security, and organization migration.

Scope

• Add the account model to this repository.
• Link it from the community and profile entrypoints.
• Align repository-specific contribution guides on ready tasks and small unplanned fixes.
• Publish .github first so dependent links never point to a missing document.

No local task needed: this is a focused account-infrastructure documentation correction requested directly by the maintainer.