🧪 test: Add missing error path coverage for crawlCanvasCourse

[savvides]

🎯 What: The testing gap addressed
The crawlCanvasCourse validation logic for missing origin and courseId inside extension/background/canvas-crawler.cjs was missing an explicit unit test, reducing our confidence if validation was accidentally modified or removed.

📊 Coverage: What scenarios are now tested
This commit adds checks ensuring crawlCanvasCourse catches null/undefined appropriately:

1. crawlCanvasCourse(null, '12345') throws "Canvas origin and courseId are required for course crawling."
2. crawlCanvasCourse('https://canvas.instructure.com', null) throws "Canvas origin and courseId are required for course crawling."

✨ Result: The improvement in test coverage
The error paths for parameter validation are fully covered, helping guarantee no regressions and ensuring parameter constraints are strictly upheld moving forward.

---

PR created automatically by Jules for task 3365728774031862764 started by @savvides

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.