feat: support post-migration startup hooks (#54)

Sense/server/internal/platform/app.go

@@ -1,6 +1,7 @@
 package platform
 
 import (
+	"context"
 	"database/sql"
 	"io/fs"
 	"log/slog"
@@ -17,6 +18,20 @@ type App struct {
 	logger     *slog.Logger
 	mux        *http.ServeMux
 	migrations []Migration
+	startups   []func(context.Context) error
+}
+
+func (a *App) RegisterStartup(startup func(context.Context) error) {
+	a.startups = append(a.startups, startup)
+}
+
+func (a *App) Start(ctx context.Context) error {
+	for _, startup := range a.startups {
+		if err := startup(ctx); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 func NewApp(cfg Config, database *sql.DB, logger *slog.Logger) *App {
@@ -101,3 +116,4 @@ func requestSecurityHeaders(next http.Handler) http.Handler {
 		next.ServeHTTP(w, r)
 	})
 }
+