docs: add Hanzilla Canada internship resource

[hanzili]

Summary

• Add Hanzilla Jobs to the Useful Lists section as a Canada-specific student job-search resource.
• Link directly to the internships/co-ops landing page for Canadian students.
• Describe the scope as internships, co-ops, new-grad, junior, and entry-level roles across multiple fields, not just SWE.

Why

This guide is focused on early student opportunities. Hanzilla is a free, daily-updated Canadian companion resource for students looking for internships/co-ops and early-career roles in Canada.

Test plan

• README-only change
• git diff --check