Adds LocalLibrariesController (L1-L7: list/get/create/update/delete/move-path/
path-exists) wrapping the existing local-library MediatR commands, mapping to
the shared S0 response DTOs. Per design #202 §A.1/§C5/§C6:
- 404 for L4/L5/L6 comes from a controller pre-check (GetLocalLibraryById is
None), not the handler -- .Apply/.ToEitherAsync both .Join() a NotFoundError
into a plain 422, so relying on the handler would be dead code. This is
check-then-act; a delete racing the pre-check falls through to the handler's
422, documented in the controller.
- L4/L5 409 via IEntityLocker.IsLibraryLocked(id); L6 resolves the source
library from the path id (new ILibraryRepository.GetLibraryIdForPath) before
its own lock check.
- MoveLocalLibraryPathHandler gains same-MediaKind and different-library
validation (finding 3) -- Blazor only filtered these client-side in the move
dialog, so an API/MCP client could bypass them.
- CreateLocalLibraryHandler/UpdateLocalLibraryHandler gain a shared
NewPathsMustExist validation (LocalLibraryHandlerBase) that Directory.Exists-
checks only new paths (Id < 1); existing rows stay exempt so an unmounted
share doesn't block a rename. L7 (path-exists) is a controller-local
IFileSystem check with no command.
Tests: controller route/mediator-arg tests incl. 404-pre-check vs
fall-through-422 and 409-lock cases; handler tests for the move-path
cross-kind/same-library 422s, new-path 422 (missing/mixed), and a lossless
round-trip proving local paths are identified by normalized path string, not
id. Full solution test suite (Scanner/Core/Architecture/Tests/Infrastructure)
green, 0 regressions.
Deviations: none from the S1 slice description. Did not touch
MediaSourceRepository.cs or any Plex/Jellyfin/Emby file (S2/S3 scope). Did not
run the OpenAPI regen scripts (separate gate after S1-S3 merge per design §E).
