[Repo][Codex] Complete AI collaboration repository setup

[BotTony329]

Objective

Complete the repository collaboration infrastructure so Claude and Codex can work safely through isolated branches and reviewed pull requests without relying on shared chat history.

What changed

• Added strict agent rules, source-of-truth priority, branch workflow, and documentary ownership.
• Added concise repository, security, branching, testing, architecture, interface, decision, and handoff documentation.
• Added controlled bug and feature-task issue forms plus a comprehensive pull request template.
• Added the Claude/Codex task register with future tasks left waiting or blocked.
• Added the repository-validation GitHub Actions workflow for required files, common secrets, oversized files, YAML, and JSON.
• Preserved the existing Godot .gitignore; no gameplay or Godot scripts were added.

Validation

• Required-file and non-empty-file checks pass.
• YAML and JSON parsing pass.
• Local Markdown links resolve.
• Common-secret scan passes.
• Oversized-file scan passes.
• git diff --check passes.

Product/framework status

No approved detailed PRD, Prototype Contract, or implemented framework existed in the repository. These documents are explicitly marked as drafts where content must come from the Game Director or Claude; no missing product or architecture rules were invented.

Handoff

Claude is the next owner and should create claude/core-framework from the latest develop after this PR is reviewed and merged. No gameplay interfaces are frozen yet.