feat: Implement Statistics API with 8 endpoints under /api/v1/statistics/

- Add statistics.sql with 8 SQL queries for play count statistics
- Generate repository code via sqlc
- Add backend/statistics.go with business logic
- Add server/statistics_handler.go with Echo handlers
- Register protected routes under /api/v1/statistics/ with token auth
- Endpoints: games/most-played, games/least-played, games/never-played,
  games/last-played, games/oldest-played, songs/most-played,
  songs/least-played, summary

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/server/server.go

@@ -15,10 +15,11 @@ import (
 )
 
 type Server struct {
-	port         int
-	db          *db.Database
-	tokenHandler *TokenHandler
-	httpServer  *http.Server
+	port            int
+	db             *db.Database
+	tokenHandler   *TokenHandler
+	statisticsHandler *StatisticsHandler
+	httpServer     *http.Server
 }
 
 var (
@@ -67,12 +68,16 @@ func NewServerInstance() *Server {
 
 	// Initialize token handler with database pool
 	tokenHandler := NewTokenHandler(database.Pool)
+	
+	// Initialize statistics handler
+	statisticsHandler := NewStatisticsHandler()
 
 	// Create the server instance
 	appServer := &Server{
-		port:         port,
-		db:          database,
-		tokenHandler: tokenHandler,
+		port:            port,
+		db:             database,
+		tokenHandler:   tokenHandler,
+		statisticsHandler: statisticsHandler,
 	}
 
 	// Create the HTTP server