feat: Sites feature backend

docs/architecture.md

@@ -69,6 +69,12 @@ The use cases `ListActivity`, `GetActivitySummary` and `ExportActivity` turn the
 
 Producers: `ArticleChanges`, `TextChange` and `BodyChange` in `internal/domain/audit` build the change lists (the body change holds only a signed rune count delta), and `NewTarget` and `ReleaseTarget` build the target snapshots (types `article`, `image`, `user`, `invite`, `api_key`, `release`). The use cases create, edit, publish, unpublish and delete article, upload, rename, delete, merge and purge media, register, verify, update profile, create, cancel, renew and accept invite, check, download and restart take the request context first and an `audit.Recorder` last, and record exactly one event after the change or the refusal (the action catalogue is in `docs/api.md`). Events are never written by handlers, middleware or GORM hooks, and nothing is recorded for reads or for a target that does not exist. `useCases/auditFailures.go` holds the fixed table of failure sentences keyed by domain `Err...` sentinels (matched with `errors.Is`, each at most 255 characters; the restart action overrides `ErrJobInProgress`) with the generic fallback "Something went wrong on our side. Please try again."; raw error text is never stored. The manual purge runs the groups through the non-recording `MergeMediaUseCase.merge`, so only one `media.purge` event is written; `RunPurgeUseCase.Execute` is the non-recording run that `PurgeSchedulerUseCase.Tick(now)` uses to record one `system.media_purge` event with the system actor and `context.Background()`. `StartUpdateDownloadUseCase` hands `context.WithoutCancel(ctx)` to its job goroutine so the `system.update_downloaded` event, written when the job becomes `ready` or `failed`, keeps the origin of the request. `middleware.AuditContext` is mounted on the article, user, media and system routers (after the API key middleware where keys are accepted), so API key calls are attributed to the key.
 
+### Sites
+
+`internal/domain/site` holds the `Site` entity (name, immutable key, normalised base URL, optional default social image, `index` or `noindex` robots, optional locale, the default flag and the computed `article_count`), `NormalizeBaseURL`, `SeedBaseURL`, `NormalizeLocale`, `IsValidKey`, the `Patch` type (with `Nullable` for the two nullable fields), the `Err...` sentinels (`ErrSiteNotFound`, `ErrSiteKeyTaken`, `ErrSiteHasArticles`, `ErrDefaultSite`, `ErrKeyImmutable`, `ErrInvalidSiteURL`, `ErrInvalidLocale`, `ErrUseSetDefault`, `ErrInvalidReassign`) and the `Repository` interface. `persistence.SiteRepository` implements it over `models.Site` (`sites`, unique `site_key`); the single default is kept by the transactional operations `Create` (when flagged) and `SetDefault`, not by an index, and `DeleteMovingArticles` moves the articles and deletes the site in one transaction. Articles carry a `site_id` (indexed, no foreign key, so the SQL stays portable).
+
+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`.
+
 ### 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`.