docs: add Canadian internship resource

[hanzili]

Summary

• Add a Canada-specific internship/new-grad jobs resource to the guide's Resources section
• Link to Hanzilla Jobs' internships page, which is a free daily-updated Canadian student/recent-grad job board across internships, co-ops, new-grad, junior, and entry-level roles

Why

The guide already lists internship supply/startup internship resources. This adds a small regional resource for students looking specifically in Canada.

Test plan

• Markdown-only change
• git diff --check passed