feat: Authors feature backend (and upgraded deprecated mods)

docs/architecture.md

@@ -75,6 +75,12 @@ Producers: `ArticleChanges`, `TextChange` and `BodyChange` in `internal/domain/a
 
 The use cases `ListSites`, `CreateSite`, `UpdateSite`, `SetDefaultSite` and `DeleteSite` live in `internal/infrastructure/useCases`; the article, media and purge use cases take the site repository as a required constructor argument, wired by the composition root (new articles take the default site, `UpdateArticle` moves an article and records `site` with site names, the media use cases count, clear and repoint default social images). `api/handlers/site` serves `/v1/site`; reads accept a session or an API key, writes are session only behind `RequireOwner`. `database.Migrate(db, publicURL)` registers the model, seeds one default site from `PUBLIC_URL` when the table is empty and backfills `articles.site_id`.
 
+### Authors
+
+`internal/domain/author` holds the `Author` entity (name, unique slug, bio, optional avatar, optional website, social links, the unique optional `user_id`, `is_linked`, the computed `article_count` and a `user_email` that only owner and admin responses carry), the public `Byline` shape embedded in articles, the `Patch` type, the slug generation (a hand-written Latin diacritic folding table, no external dependency), the value rules (`ValidateBio`, `ValidateURL`, `ValidateLinks`, `IsValidSlug`, `IsValidName`), the `Err...` sentinels (`ErrAuthorNotFound`, `ErrSlugTaken`, `ErrAuthorHasArticles`, `ErrUserAlreadyLinked`, `ErrAuthorAlreadyLinked`, `ErrAuthorRights`, `ErrBioTooLong`, `ErrInvalidURL`, `ErrTooManyLinks`, `ErrInvalidSlug`, `ErrInvalidReassign`) and the `Repository` interface. `persistence.AuthorRepository` implements it over `models.Author` (`authors`, unique `slug` and unique nullable `user_id`) and the ordered join `models.ArticleAuthor` (`article_authors`, unique `(article_id, author_id)` and a `position`); uniqueness is checked inside the transaction and re-explained after a failed write, so a race still answers a domain sentinel, and `DeleteMovingCredits` moves the credits (keeping the position, never duplicating) and deletes the author in one transaction. `ArticleRepository` attaches the ordered `Byline`s to the articles it returns, writes `author_ids` in the article update transaction and removes the credits when an article is deleted.
+
+The use cases `ListAuthors`, `CreateAuthor`, `CreateMyAuthor`, `UpdateAuthor`, `DeleteAuthor` and `GetMyAuthor` live in `internal/infrastructure/useCases`; `CreateArticle` credits the creator's author, `UpdateArticle` validates and records `author_ids`, and the media, purge and activity use cases take the author repository as a required constructor argument (avatars count as media usage, are cleared on delete and repointed on merge and purge). `api/handlers/author` serves `/v1/author`: the list accepts a session or an API key, every write is session only, `POST /` and `DELETE` sit behind `RequireOwnerOrAdmin`, and the edit rights (owner or admin, or the caller's own linked author) are decided by `UpdateAuthor` from the caller the handler passes in. `GET /v1/auth/me` adds the linked author through `GetMyAuthor`.
+
 ### Image variants
 
 `internal/domain/image` holds the `Variant` entity and its rules (`VariantSettings.Normalized`, the settings `Fingerprint`, `VariantETag`, `ETagMatches`, `IsAnimatedGIF`), the sentinels (`ErrVariantNotFound`, `ErrVariantExists`, `ErrVariantInvalid`, `ErrVariantFormatUnavailable`, `ErrUnknownVariant`, `ErrUnsupportedParameter`, `ErrSourceTooLarge`) and three ports: `VariantRepository` (definitions), `VariantFileRepository` (the index of generated files: variant name, source stored name, cached stored name, content type, size and the settings fingerprint, needed because `Storage.Put` chooses the stored name itself) and `VariantRenderer` (decode a source, encode a variant, report the formats it can encode). `internal/infrastructure/imaging` is the renderer adapter, free of GORM and HTTP; the persistence adapters are `VariantRepository` and `VariantFileRepository` over `models.ImageVariant` and `models.ImageVariantFile`.