Refactor front end files

[chaunmt]

• Refactor routing and layout following app's conventions.
• Handling not found and wrong route correctly.
• Adding placeholder components waiting for designs.
• Fix some metadata.
• Delete unused CSS for bgImg.

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Name	Status	Preview	Comments	Updated (UTC)
course-flowchart	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Sep 23, 2024 9:07pm