Enforce English-only GitHub tasks at the forge

[gHashTag]

Contract

• Reject new issue titles or bodies containing non-ASCII letters.
• Keep punctuation, Markdown, URLs, paths, and emoji available.
• Close invalid issues automatically regardless of whether they came from Queen, CLI, or the web.
• Install strict Lefthook checks for task language, commit subjects, agent trailers, and branch names.

Evidence

• Policy self-test passes.
• English fixture passes.
• Non-English fixture is refused.
• Workflow and Lefthook YAML parse successfully.

Closes #1291