Add an LLM based spam filter

[daniel-lerch]

This pull request adds a spam filter that can be enabled for each distribution list individually and classifies emails using Mistral AI.

Resolves #94

[Copilot]

Pull request overview

This PR introduces an optional, per-distribution-list spam filter backed by Mistral AI, and replaces the previous single newsletter boolean with a more extensible flags object for distribution list behavior.

Changes:

• Add flags (override recipient, spam filter) to distribution list API + web UI and update forwarding behavior accordingly.
• Implement server-side LLM spam classification with MIME text extraction (plain + HTML) and persist classification results on inbound emails.
• Add EF Core migration for spam classification fields and add tests/resources for spam filtering and text extraction.

Reviewed changes

Copilot reviewed 27 out of 30 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
webapp/src/views/EditDistributionList.vue	Replaces newsletter with two flag checkboxes and sends flags payload on save.
webapp/src/views/DistributionLists.vue	Displays icons for enabled distribution list flags in the table.
webapp/src/services/distribution-list.ts	Changes create/modify request type to include flags object.
webapp/package-lock.json	Updates minimum Node engine version.
server/Mailist/SpamFilter/SpamFilterService.cs	New service that builds prompts, calls the LLM, and deserializes classification JSON.
server/Mailist/SpamFilter/SpamFilterOptions.cs	Adds configuration options for enabling and configuring the spam filter.
server/Mailist/SpamFilter/SpamCategory.cs	Defines classification categories used by the spam filter and email processing.
server/Mailist/SpamFilter/MimeTextExtractionService.cs	Extracts text from MIME bodies (plain/html) for LLM input.
server/Mailist/Models/Json/DistributionList.cs	Replaces Newsletter with a Flags object in API models; adds conversion helpers.
server/Mailist/Migrations/DatabaseContextModelSnapshot.cs	Updates snapshot for unique index change and new inbox email spam fields.
server/Mailist/Migrations/20260331155808_SpamFilter.Designer.cs	New migration designer snapshot for schema changes.
server/Mailist/Migrations/20260331155808_SpamFilter.cs	Adds spam category/justification columns; switches alias uniqueness constraint to unique index.
server/Mailist/Mailist.csproj	Adds AngleSharp + Mistral SDK dependencies; bumps JWT package version.
server/Mailist/Extensions/IServiceCollectionExtensions.cs	Binds and validates SpamFilter options section.
server/Mailist/EmailRelay/MimeMessageCreationService.cs	Adds rejection message generation for spam-filtered emails.
server/Mailist/EmailRelay/Entities/InboxEmail.cs	Adds SpamCategory and SpamJustification fields to the inbox email entity.
server/Mailist/EmailRelay/EmailRelayJobController.cs	Integrates spam classification into the relay pipeline and updates forwarding flag behavior.
server/Mailist/EmailRelay/DistributionListFlags.cs	Renames newsletter flag to OverrideRecipient and adds SpamFilter.
server/Mailist/DatabaseContext.cs	Updates EF mappings for distribution list alias uniqueness and spam category conversion.
server/Mailist/Controllers/DistributionListController.cs	Updates API to accept/return Flags object instead of Newsletter.
server/Mailist/appsettings.json	Adds SpamFilter configuration block (disabled by default).
server/Mailist.Tests/SpamFilterServiceTests.cs	Adds (optional) tests that call the real LLM when enabled via config.
server/Mailist.Tests/Resources/23437.header	Adds embedded test email header fixture (spam example).
server/Mailist.Tests/Resources/23437.body	Adds embedded test email body fixture (spam example).
server/Mailist.Tests/Resources/23377.header	Adds embedded test email header fixture (legit example).
server/Mailist.Tests/Resources/23377.body	Adds embedded test email body fixture (legit example).
server/Mailist.Tests/MimeTextExtractionServiceTests.cs	Adds unit test validating HTML-to-text compression.
server/Mailist.Tests/Mailist.Tests.csproj	Embeds .body/.header resources into the test assembly.
server/Mailist.Tests/Integration/DistributionListIntegrationTests.cs	Updates integration tests to use new Flags API.
.vscode/settings.json	Adds Tailwind CSS file association.

Files not reviewed (2)

• server/Mailist/Migrations/20260331155808_SpamFilter.Designer.cs: Language not supported
• webapp/package-lock.json: Language not supported

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