Add alternative names and cover art for soundtracks

Alternative names (#32):
- PUT /api/v1/soundtracks/{uuid}/alternative-names replaces a soundtrack's
  alternative names (trimmed, deduplicated, without the soundtrack's own name).
- alternative_names is in the soundtrack and statistics responses.
- /find matches them too and shows which name matched.

Covers (#12), stored in COVERS_PATH and off when it is not set:
- GET, PUT (upload) and DELETE /api/v1/soundtracks/{uuid}/cover, and
  PUT .../cover/source to pick a SteamGridDB game or AniList anime by ID.
  Uploaded and picked covers are never replaced automatically.
- With STEAMGRIDDB_API_KEY, a background job searches SteamGridDB, then
  AniList, by name, alternative names and the name without bracketed parts,
  at startup, after a sync and after names change. Search results are ranked
  by matching words, so "Civilization IV" gets "Sid Meier's Civilization IV".
- cover_modified (Unix seconds) is in the soundtrack and statistics responses,
  so clients can cache covers.

The new columns are added to migration 000006, which is not released yet.

Closes #12, closes #32

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/cover_handler.go

@@ -0,0 +1,114 @@
+package server
+
+import (
+	"context"
+	"net/http"
+
+	"music-server/internal/backend"
+
+	"github.com/danielgtaylor/huma/v2"
+	"github.com/google/uuid"
+)
+
+type coverUploadInput struct {
+	UUID    string `path:"uuid" format:"uuid" doc:"UUID of the soundtrack"`
+	RawBody []byte `contentType:"image/*" doc:"The image: JPEG, PNG or WebP, at most 10 MB"`
+}
+
+// CoverSource is the body of PUT /soundtracks/{uuid}/cover/source.
+type CoverSource struct {
+	Source string `json:"source" enum:"steamgriddb,anilist" doc:"Where the cover comes from"`
+	ID     string `json:"id" minLength:"1" maxLength:"50" doc:"The game's ID on SteamGridDB, or the anime's ID on AniList"`
+}
+
+type coverSourceInput struct {
+	UUID string `path:"uuid" format:"uuid" doc:"UUID of the soundtrack"`
+	Body CoverSource
+}
+
+func (s *Server) registerCovers(a huma.API) {
+	op := func(id, method, path, summary, description string, errs ...int) huma.Operation {
+		return huma.Operation{
+			OperationID: id,
+			Method:      method,
+			Path:        path,
+			Summary:     summary,
+			Description: description,
+			Tags:        []string{"covers"},
+			Errors:      errs,
+		}
+	}
+	// covers returns the cover service, or ErrCoversDisabled when COVERS_PATH is not set.
+	covers := func() (*backend.CoverService, error) {
+		if s.covers == nil {
+			return nil, apiError(backend.ErrCoversDisabled)
+		}
+		return s.covers, nil
+	}
+
+	get := op("get-soundtrack-cover", http.MethodGet, "/soundtracks/{uuid}/cover", "Soundtrack cover",
+		"Returns the soundtrack's cover image. cover_modified in the soundtrack responses tells when it last changed.",
+		http.StatusNotFound)
+	get.Responses = fileResponses("The cover image", "image/jpeg", "image/png", "image/webp")
+	register(s, a, route{op: get},
+		func(ctx context.Context, in *uuidInput) (*huma.StreamResponse, error) {
+			if s.covers == nil {
+				return nil, huma.Error404NotFound("Not Found")
+			}
+			path, err := s.covers.Path(ctx, in.id())
+			if err != nil {
+				return nil, apiError(err)
+			}
+			return streamFile(path, "", false)
+		})
+
+	upload := op("upload-soundtrack-cover", http.MethodPut, "/soundtracks/{uuid}/cover", "Upload a cover",
+		"Stores the image as the soundtrack's cover. The automatic search never replaces it; delete it to go back to automatic.",
+		http.StatusBadRequest, http.StatusNotFound, http.StatusServiceUnavailable)
+	upload.MaxBodyBytes = backend.MaxCoverBytes
+	upload.DefaultStatus = http.StatusNoContent
+	register(s, a, route{op: upload},
+		func(ctx context.Context, in *coverUploadInput) (*struct{}, error) {
+			c, err := covers()
+			if err != nil {
+				return nil, err
+			}
+			if err := c.Upload(ctx, uuid.MustParse(in.UUID), in.RawBody); err != nil {
+				return nil, apiError(err)
+			}
+			return nil, nil
+		})
+
+	source := op("set-soundtrack-cover-source", http.MethodPut, "/soundtracks/{uuid}/cover/source", "Pick a cover",
+		"Downloads the cover of the given SteamGridDB game or AniList anime and stores it as the soundtrack's cover. "+
+			"The automatic search never replaces it. SteamGridDB needs STEAMGRIDDB_API_KEY on the server.",
+		http.StatusBadRequest, http.StatusNotFound, http.StatusBadGateway, http.StatusServiceUnavailable)
+	source.DefaultStatus = http.StatusNoContent
+	register(s, a, route{op: source},
+		func(ctx context.Context, in *coverSourceInput) (*struct{}, error) {
+			c, err := covers()
+			if err != nil {
+				return nil, err
+			}
+			if err := c.FromSource(ctx, uuid.MustParse(in.UUID), in.Body.Source, in.Body.ID); err != nil {
+				return nil, apiError(err)
+			}
+			return nil, nil
+		})
+
+	remove := op("delete-soundtrack-cover", http.MethodDelete, "/soundtracks/{uuid}/cover", "Remove the cover",
+		"Deletes the soundtrack's cover, including one set by hand, so the automatic search looks for a new one.",
+		http.StatusNotFound, http.StatusServiceUnavailable)
+	remove.DefaultStatus = http.StatusNoContent
+	register(s, a, route{op: remove},
+		func(ctx context.Context, in *uuidInput) (*struct{}, error) {
+			c, err := covers()
+			if err != nil {
+				return nil, err
+			}
+			if err := c.Remove(ctx, in.id()); err != nil {
+				return nil, apiError(err)
+			}
+			return nil, nil
+		})
+}