Add applicant editing functionality

[anshagnihotry258]

Changes

• Added editing for existing applicants
• Added editing of applicant remarks
• Allows editing accepted/rejected applicants
• Preserves applicant decision status while editing
• Added complete applicant data loading before editing
• Walk-in editing remains supported

Testing

• Tested locally with yarn dev
• Verified accepted applicants can be edited
• Verified rejected applicants can be edited
• Verified remarks persist after saving

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