Add Canadian English requirement to AGENTS.md

[ScottMorris]

Context

The Liminal HQ org uses Canadian English spelling across all repos, commit messages, and documentation. This is explicitly documented in the org's AGENTS.md files.

This repo's AGENTS.md does not mention the Canadian English requirement. Before org transfer, this should be aligned.

Examples

• colour not color
• behaviour not behavior
• organise / organised not organize / organized
• analyse not analyze
• centre not center
• licence (noun) / license (verb)
• cancelled not canceled

Proposal

Add a Canadian English spelling section to AGENTS.md.

Acceptance Criteria

• AGENTS.md updated with Canadian English requirement
• Existing content reviewed for spelling alignment