add sqlc, fix background img fetching

grpc-backend/sqlc/query/beatmap.sql

@@ -0,0 +1,30 @@
+-- name: InsertBeatmap :exec
+INSERT INTO Beatmap (
+    BeatmapId, Artist, ArtistUnicode, Title, TitleUnicode, Creator,
+    Difficulty, Audio, MD5Hash, File, RankedStatus, 
+    LastModifiedTime, TotalTime, AudioPreviewTime, BeatmapSetId, 
+    Source, Tags, LastPlayed, Folder
+) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?);
+
+-- name: GetBeatmapByHash :one
+SELECT * FROM Beatmap WHERE MD5Hash = ?;
+
+-- name: GetBeatmapCount :one
+SELECT COUNT(*) FROM Beatmap;
+
+-- name: GetRecentBeatmaps :many
+SELECT BeatmapId, MD5Hash, Title, Artist, Creator, Folder, File, Audio, TotalTime
+FROM Beatmap GROUP BY Folder ORDER BY LastModifiedTime DESC LIMIT ? OFFSET ?;
+
+-- name: SearchBeatmaps :many
+SELECT BeatmapId, MD5Hash, Title, Artist, Creator, Folder, File, Audio, TotalTime 
+FROM Beatmap 
+WHERE Title LIKE ? OR Artist LIKE ? 
+LIMIT ? OFFSET ?;
+
+-- name: GetArtists :many
+SELECT Artist, COUNT(Artist) AS count
+FROM Beatmap 
+WHERE Artist LIKE ? OR Title LIKE ?
+GROUP BY Artist 
+LIMIT ? OFFSET ?;