chore: Revert back to season-year based slug for notes to avoid future slug misdirects and 404s (first tech-debt)

[Gurpranked]

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Description:

Reduce the potential for slug mangling by restricting the /current-schedule to only the latest semester's primary schedule. That way the notes won't have the requirement to have their slugs changed every semester. Reduce toil in creating notes, improves long-term consistency of notes links, and preemptively reduces the potential for slugs getting complicated.

Type of Contribution:

• New topic or explanation
• Practice questions
• Study guide
• Other (please specify): Reduce the potential for slug mangling.

Related Issues or References:

Slug mangling (not sure if that's the official term for it, but it conveys the idea)

Verification:

• I confirm that no class materials, solutions, or professor-provided content are included without explicit permission.

Additional Information:

N/A

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