feat(recommendation): add LoadCandidates DB-backed loader

Wraps the LoadRadioCandidates sqlc query, projects rows to
[]Candidate. Live-DB tests verify seed exclusion, recently-played
exclusion, stat-join correctness (likes + plays + skips +
last_played_at), and cross-user isolation.

internal/recommendation/candidates.go

@@ -0,0 +1,44 @@
+package recommendation
+
+import (
+	"context"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+)
+
+func LoadCandidates(
+	ctx context.Context,
+	q *dbq.Queries,
+	userID, seedID pgtype.UUID,
+	recentlyPlayedHours int,
+) ([]Candidate, error) {
+	rows, err := q.LoadRadioCandidates(ctx, dbq.LoadRadioCandidatesParams{
+		UserID:  userID,
+		ID:      seedID,
+		Column3: float64(recentlyPlayedHours),
+	})
+	if err != nil {
+		return nil, err
+	}
+	out := make([]Candidate, 0, len(rows))
+	for _, r := range rows {
+		var lpt *time.Time
+		if r.LastPlayedAt.Valid {
+			t := r.LastPlayedAt.Time
+			lpt = &t
+		}
+		out = append(out, Candidate{
+			Track: r.Track,
+			Inputs: ScoringInputs{
+				IsGeneralLiked: r.IsLiked,
+				LastPlayedAt:   lpt,
+				PlayCount:      int(r.PlayCount),
+				SkipCount:      int(r.SkipCount),
+			},
+		})
+	}
+	return out, nil
+}