refactor: separate certificates data from experiences and add new Backend certificate

[CodingWithJiro]

Description

Separated certificate data from the experiences data source and updated pages to use the new structure. I also added my newly acquired Back-End Development and APIs certification.

Changes

• Created a dedicated certificates.ts data file.
• Moved certificate data out of experiences.ts.
• Added Back-End Development and APIs certification.
• Updated imports to use the new certificates data.
• Created tests for the certificates data.
• Updated Experiences tests after removing certificate data.
• Displayed certificates from latest to oldest in /certificates page.
• Updated certificate page naming and latest certificate image.

Notes for Reviewers

• Certificates are now maintained independently from experience data so it's easier for me to add new data whenever possible.
• This is short PR for updating my recent certifications.
• Also, I tested Google Analytics and it works!
• I would definitely update the README.md file next.

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Project	Deployment	Actions	Updated
elmarchavez	Ready	Preview	Oct 2, 2026 8:32am UTC

[CodingWithJiro]

In a team setting, this PR would await senior developer approval.
For this solo project, I’ll proceed with merging after review.