feat(M003/S03): play count column + data pipeline

Backend:
- GetAllTracksWithFullMetadata queries now select play_count and last_played
- mapTrackRow accepts and passes through PlayCount/LastPlayed
- PlayCount + LastPlayed added to library.Track struct
- sqlcgen Row types updated with new fields

Frontend:
- PlayCount + LastPlayed added to library.Track TypeScript model
- 'Plays' column added to track-list column definitions (60px, right-aligned, sortable)

Queries without play data (search, genre, album) pass 0/empty defaults.

frontend/src/components/track-list/columns.ts

@@ -186,6 +186,16 @@ export const COLUMN_DEFS: Record<string, ColumnDef> = {
         comparator: (a, b) =>
             compareNum(a.FileSize, b.FileSize),
     },
+    playCount: {
+        id: 'playCount',
+        label: 'Plays',
+        accessor: (t) =>
+            t.PlayCount ? String(t.PlayCount) : '',
+        defaultWidth: '60px',
+        align: 'right',
+        comparator: (a, b) =>
+            compareNum(a.PlayCount, b.PlayCount),
+    },
 };
 
 /**

frontend/wailsjs/go/models.ts

@@ -266,6 +266,8 @@ export namespace library {
 	    Channels: number;
 	    Bitrate: number;
 	    FileSize: number;
+	    PlayCount: number;
+	    LastPlayed: string;
 	
 	    static createFrom(source: any = {}) {
 	        return new Track(source);
@@ -289,6 +291,8 @@ export namespace library {
 	        this.Channels = source["Channels"];
 	        this.Bitrate = source["Bitrate"];
 	        this.FileSize = source["FileSize"];
+	        this.PlayCount = source["PlayCount"];
+	        this.LastPlayed = source["LastPlayed"];
 	    }
 	}