fix: preserve typed API error prototypes

[saurabhhhcodes]

Summary\n- keep typed API errors intact through the handler chain\n- avoid prototype loss when middleware rethrows errors\n\n## Validation\n- reviewed the single-line API handler diff\n- no other files changed

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🔨 Latest commit	f5da3d1

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👷 Deploy request for docmagic1 pending review.

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🔨 Latest commit	f5da3d1

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📥 Commits

Reviewing files that changed from the base of the PR and between ff793ac and f5da3d1.

📒 Files selected for processing (10)

• app/api/documents/route.ts
• app/api/generate/letter/route.ts
• app/api/generate/presentation/route.ts
• app/api/generate/resume/route.ts
• app/api/send-email/route.ts
• jest.config.mjs
• jest.polyfills.cjs
• lib/api-handler.ts
• lib/error-handler.ts
• lib/validation.ts

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[Muneerali199]

@SaurabhhCodes please rebase on latest main to resolve conflicts