feat: entity enrichment, test coverage, email notifications & production Dockerfile

[Azfe]

Summary

This PR consolidates multiple development epics into a production-ready release:

• New entity fields across Work Experience, Education, Additional Training and Projects
• Email notification system via Resend (replacing SendGrid/SMTP)
• Massive test coverage expansion — from ~95% to ~100% unit coverage across all layers
• Production Dockerfile ready for Railway deployment
• Bug fixes in repository update methods, optional fields handling, and CV aggregation

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Changes by area

Domain

• WorkExperience: add location, is_current, duration_months fields
• Education & AdditionalTraining: add optional technologies field
• Project: add optional image_url field
• Skill: remove category field across all layers
• Tool: make category optional

Application / Infrastructure

• GetCompleteCVUseCase: fix aggregation to include all entities using default_profile
• CreateContactMessageUseCase: integrate email notification on new message
• Repository update() methods: fix bug where _id was included in the replacement document
• SkillUseCase: fix order_index propagation through the full PUT pipeline
• Email service: replace SendGrid + aiosmtplib with ResendEmailService; add NullEmailService for non-production
  environments
• IEmailService interface added to shared/interfaces/

API

• Schemas updated for all enriched entities (WorkExperienceRequest, ProjectRequest, etc.)
• ToolBase.category made optional
• SkillSchema: remove category references

Testing

• 136 files changed, +9 438 lines — new unit tests for every use case, DTO, repository, mapper, value object and
  exception class
• Integration & E2E fixtures updated to match schema changes

Infrastructure / Deployment

• Dockerfile (production) created for Railway — python:3.13-slim, no --reload
• requirements.txt converted from UTF-16 to UTF-8; cleaned up
• .env.example updated with Resend variables

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Testing checklist

• make test passes with no failures inside the container
• Unit coverage remains at or above 96%
• Integration tests pass against a real MongoDB instance
• E2E test_complete_cv_flow.py passes end-to-end
• POST /api/v1/contact-messages triggers an email via Resend (staging key)
• GET /api/v1/cv returns all sections including location, technologies, image_url
• GET /api/v1/skills returns skills without category field