Validate referral invite emails before throttling

[absalonCRC]

Summary

• fixes bug: referral invite validation reports rate limits for invalid email batches #143
• validates normalized invite email syntax before rate-limit and duplicate checks
• uses only valid invite recipients for throttle math, duplicate lookup, inserts, and email sends
• adds regression coverage for invalid batches that previously returned a misleading rate-limit error

Why

The referral invite API applied hourly/daily invite limits before proving that any submitted email was usable. A batch of invalid email strings could return 429 Too many invites instead of a 400 validation error.

Validation

• pnpm test:run src/app/api/referrals/route.test.ts
• pnpm exec eslint src/app/api/referrals/route.ts src/app/api/referrals/route.test.ts
• pnpm type-check
• git diff --check

Payment for the active uGig affiliate testing bounty can go to SOL: 27sdMYXofqoM9qR13bZhccRNYeEgYn5EoHXTSJn4QWKP.

Payment fallback: PayPal cultofrozen@gmail.com

[absalonCRC]

Maintainer note for the active uGig affiliate/referral testing bounty (4741218f-a723-46bb-82cb-6516120331ae): I have a clean stack of focused bug-fix PRs ready for review, all with Socket checks passing and no review comments so far.

Clean PRs submitted for this bounty:

• Guard referral storage access #126 Guard referral storage access
• Use current origin for referral links #128 Use current origin for referral links
• Add referral link copy fallback #130 Add referral link copy fallback
• Recover from referral invite send failures #132 Recover from referral invite send failures
• Disable referral copy until link loads #134 Disable referral copy until link loads
• Fix affiliate tracking URL origin #136 Fix affiliate tracking URL origin
• Validate affiliate edit product URLs #138 Validate affiliate edit product URLs
• Validate affiliate conversion sat amounts #140 Validate affiliate conversion sat amounts
• Validate referral invite email types #142 Validate referral invite email types
• Validate referral invite emails before throttling #144 Validate referral invite emails before throttling
• Validate affiliate application notes #146 Validate affiliate application notes
• Validate affiliate offer edit text fields #148 Validate affiliate offer edit text fields
• Fix affiliate category None option #152 Fix affiliate category None option
• Add affiliate dashboard copy fallback #154 Add affiliate dashboard copy fallback
• Add affiliate tracking link copy fallback #157 Add affiliate tracking link copy fallback
• Return tracking link for existing affiliate applications #161 Return tracking link for existing affiliate applications
• Handle malformed affiliate application bodies #164 Handle malformed affiliate application bodies

Payment address for the bounty: SOL 27sdMYXofqoM9qR13bZhccRNYeEgYn5EoHXTSJn4QWKP.

Happy to adjust any of these if you prefer a different validation/error-handling style.