refactor: reorganize project structure and update configurations

- Move migrations/ to database/schema/ for clarity on database schema definitions
- Move sqlc.yaml to internal/database/ to group with database code
- Move static/ to cmd/server/static/ to co-locate with server
- Update all configuration files and documentation
- Follow Go project conventions for better organization

cmd/server/main.go

@@ -84,6 +84,9 @@ func main() {
 	authGroup.PUT("/theme", authHandler.UpdateTheme)
 	// force rebuild
 
+	// Static files
+	e.Static("/static", "static")
+
 	// Routes
 	handlers.SetupRoutes(protected, queries)