feat(server/m7-353): admin endpoints for cover refetch (per-album + bulk)

Adds POST /api/admin/albums/{id}/cover/refetch (synchronous single-album
retry) and POST /api/admin/covers/refetch-missing (async bulk drain).
Wires coverart.Enricher through server.New → api.Mount → handlers struct.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/admin_covers.go

@@ -0,0 +1,74 @@
+package api
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/jackc/pgx/v5"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/coverart"
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+)
+
+type adminCoverRefetchResp struct {
+	AlbumID        string  `json:"album_id"`
+	CoverArtPath   *string `json:"cover_art_path"`
+	CoverArtSource *string `json:"cover_art_source"`
+}
+
+// handleAdminAlbumRefetchCover implements POST /api/admin/albums/{id}/cover/refetch.
+// Synchronously clears + re-runs the enricher for one album.
+func (h *handlers) handleAdminAlbumRefetchCover(w http.ResponseWriter, r *http.Request) {
+	albumID, ok := parseUUID(chi.URLParam(r, "id"))
+	if !ok {
+		writeErr(w, http.StatusBadRequest, "bad_request", "invalid album id")
+		return
+	}
+	if err := h.coverart.RetryAlbum(r.Context(), albumID); err != nil {
+		if errors.Is(err, coverart.ErrNotFound) || errors.Is(err, pgx.ErrNoRows) {
+			writeErr(w, http.StatusNotFound, "not_found", "album not found")
+			return
+		}
+		h.logger.Error("admin: cover refetch failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "refetch failed")
+		return
+	}
+	row, err := dbq.New(h.pool).GetAlbumWithFirstTrackPath(r.Context(), albumID)
+	if err != nil {
+		h.logger.Error("admin: post-refetch read failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "read failed")
+		return
+	}
+	writeJSON(w, http.StatusOK, adminCoverRefetchResp{
+		AlbumID:        uuidToString(albumID),
+		CoverArtPath:   row.CoverArtPath,
+		CoverArtSource: row.CoverArtSource,
+	})
+}
+
+type adminBulkRefetchResp struct {
+	Queued int `json:"queued"`
+}
+
+// handleAdminBulkRefetchCovers implements POST /api/admin/covers/refetch-missing.
+// Returns immediately; actual drain runs in a background goroutine bounded by
+// the configured backfill cap.
+func (h *handlers) handleAdminBulkRefetchCovers(w http.ResponseWriter, r *http.Request) {
+	cap := h.coverArtBackfillCap
+	q := dbq.New(h.pool)
+	rows, err := q.ListAlbumsRetryMissing(r.Context(), int32(cap))
+	if err != nil {
+		h.logger.Error("admin: bulk count failed", "err", err)
+		writeErr(w, http.StatusInternalServerError, "server_error", "count failed")
+		return
+	}
+	go func() {
+		bgCtx := context.Background()
+		if _, err := h.coverart.EnrichRetryMissing(bgCtx, cap); err != nil {
+			h.logger.Warn("admin: bulk cover refetch failed", "err", err)
+		}
+	}()
+	writeJSON(w, http.StatusOK, adminBulkRefetchResp{Queued: len(rows)})
+}