docs(agents): expand AGENTS.md with guidelines and standards

[aheritier]

Add project agent guidelines section covering code quality
standards, working approach, and validation requirements to
help AI agents and contributors understand expectations.

Update command list formatting from hyphens to em dashes for
improved readability and visual consistency throughout the
document.

[docker-agent]

Assessment: 🟢 APPROVE

Reviewed the changes to AGENTS.md. The PR expands the document with new sections covering Code Quality Standards, Working Approach, Validation Requirements, and Git Practices, and updates command list separators from hyphens (-) to em dashes (—) for improved readability.

No issues found in the changed code. The added guidelines are clear, consistent, and aligned with project conventions. The em dash formatting is applied uniformly across all updated entries.

Note: Lines 69–71 use ./bin/docker agent (with a space) instead of ./bin/docker-agent for the serve subcommands, which may be incorrect — but this is a pre-existing issue that was not introduced by this PR, so it's out of scope for this review.