Wire risk alert email after document analysis

[bingmokaka]

Summary

• inject MailService and UsersService into the analyze job processor
• send risk alert emails only when document analysis returns one or more flags
• catch and log email delivery failures so analysis jobs still complete

Verification

• nest build passes after temporarily exposing the existing transitive dotenv package under pnpm strict resolution
• note: the repo manifest does not declare dotenv directly even though src/main.ts imports it, so plain pnpm build is blocked by that pre-existing dependency declaration issue

Closes #781

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